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ROLE OF NON-PROTEIN AMINO ACIDS IN AUTOIMMUNE DISEASES

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Abstract

Many nonprotein amino acids (NPAAs) are plant secondary metabolites and have a similar chemical structure , size, shape and charge to protein amino acids and can be mistakenly used in protein synthesis, interfere in biochemical pathways, overstimulate receptors or chelate metal ions. The Consumption of a number of plants that contain NPAAs has been shown to have acutely toxic effects in humans. The consumption of some seeds or vegetables that contain NPAAs inuences some people as a trigger for some diseases or as an exacerbating factor. The effects of NPAAs on human health are not well understood. It has been observed that chimpanzees fed alfalfa and also a volunteer subject who have intake alfalfa tablets have both developed a disease with all the characteristics of lupus erythematosus ( an autoimmune disease) and by suppressing the consumption of alfalfa the disease disappears. Most of NPAAs are of plant origin; these do not form part of the primary structure of proteins, they act as antimetabolites and most are found in higher plants; they have the same basic structure as amino acids of animal origin. The substitution of a protein amino acid in protein synthesis produces abnormal proteins which generate antibodies and modication of autoantigens as mechanism to break immunological tolerance and trigger autoimmunity. Auto-antibodies formation is a characteristic of autoimmune disease. The toxic potential of NPAAs depend the amount ingested and the consumption time. Chronic exposure to NPAAs could contribute to autoimmune disease development in genetically susceptible individuals.
ROLE OF NON-PROTEIN AMINO ACIDS IN AUTOIMMUNE DISEASES
Eliseo Ruiz
Bedolla*
Clinical Laboratory. Hospital Infantil de Mexico “ Federico Gomez” Mexico city.
*Corresponding Author
Original Research Paper
Clinical Laboratory
INTRODUCTION
Plants synthesize a great number of secondary compounds that are
toxic to other forms of life; non-protein amino acids (NPAAs) may be
toxic to microorganisms, plants, insects or higher animals. Most
NPAAs have low toxicity, but their prolonged administration can be
toxic in some mammalian tissues. Some of these compounds interfere
with the metabolism of proteins amino acids and the inclusion in
specic tissues such as the skin and some organs. Thus we have
mimosine that affects the thyroid and its metabolite (indospicin)
affects the liver, skin and brain. NPAAs alter protein synthesis by
competition with protein amino acids in messenger RNA and some
have anti-nutritional effects (1,2).
The discovery in plants of amino acids that are structurally related to
comp onen ts of mamma lian central nervous system glu tamate
receptors suggests that many of the analogues of glutamic acid are
synthesized by plants; may have a signaling function “in vivo” in
addition to any protective role that they might play (3) . The most
striking example of amino acids toxicity is neurolathyrism (lathyrism)
one of the oldest neurotoxic diseases known; described by Hippocrates
on 400 BC; lathyrus sativus is an insect-resistant crop that can grow in
poor soils and in drought conditions and is often eaten in times of
famine when there is a dietary shortage of protein amino acids; this
plant contain the NPAA β-N-oxalil-L-αβ-diaminopropionic acid (B-
ODAP) (4).
There are data on leguminous crops from the V to IV centuries BC;
wheat, barley, peas, lathyrus, lentils, beans and almortas were grown.
Lathyrus sativus is still cultivated in some regions of Spain, in North
Africa and Asia. Leguminous are rich in protein in such a way that they
are used as a substitute for meat. The content of toxic factors in beans,
peas, common beans, soybeans is important (trypsin inhibitors,
tannins, lectins and NPAAs).
Nonprotein amino acids have been reported from a wide variety lot of
plants including leguminosae, liliaceae, sapindaceae, cycadaceae,
compositae, rubiaceae and lecythidaceae. However, NPAAs are most
often found in leguminous and are mainly abundant in seeds (5). The
chemical and physiological properties of some NPAAs found in plants
which have been shown to be toxic to man, livestock and domestic
animals are reviewed.
The toxicity of (NPAAs) was rst examined systematically in the early
1960s and many were found to have growth-inhibitory properties
toward microorganisms. This is because they are similar with some
of the 20 protein amino acids. Protein synthesis is a fundamental
process in all life forms, therefore by replacing an amino acid in protein
synthesis, abnormal proteins are produced, which generate antibodies
and when it has an important role in the active site of an enzyme this
result in the loss of the activity of the enzyme. These NPAAs are called
analogues amino acids and may be incorporated into proteins (6).
Diseases associated with protein misfolding or abnormal protein
synthesis such as Parkinson´s disease and amyotrophic lateral
sclerosis are predominantly sporadic (less than 10% genetic), but the
factors that cause the disease have not been identied. No causes have
been identied for many chronic diseases in humans.
Alfalfa induces autoimmunity in humans
L-canavanine is the most studied amino acid. This amino acid was
isolated of Jack beans and wilds potatoes (hedysarum alpinum); it is
also abundant in Albizzia julibrissin; and compete with L-arginine in
protein synthesis. Canavanine a structural analog of arginine, is a
NPAA naturally occurring in Leguminosae (7). In some species the
canavanine contents ranges from 10% to 13% of the seed dry weight
and constitutes more than 95% of the free amino acid nitrogen. Also is
present in various beans, clover, onions, seeds and sprouts of alfalfa
and other higher plants. An ordinary dish may contain around 25g
beans and thus is assumed the intake of canavanine would be 200mg (5 ).
Association of Systemic Lupus Erythematosus (SLE) and alfalfa was
rst reported in a volunteer who developed lupus-like autoimmunity
while ingesting alfalfa seed for a hypercholesterolemia study. This also
was observed in chimpanzees fed with alfalfa sprouts that developed
SLE. By suppressing the consumption of alfalfa disease disappeared
both in the monkeys and in the voluntary subject (8). L-canavanine,
present in alfalfa, was suspected as a cause of this phenomenon.
During the study, the subject was ingesting crushed alfalfa seeds for six
weeks. He developed moderate splenomegaly, pancytopenia, coombs
positive, autoimmune hemolytic anemia and antinuclear antibodies
(ANA) (9). When alfalfa seeds ingestion was discontinued the spleen
size and the laboratory abnormalities returned to normal. Following
these observations, six cases of subjects who developed SLE
disease were reported from the consumption of alfalfa tablets for 3
weeks to 7 months (10). All the patients presented ANA and anti-
Many nonprotein amino acids (NPAAs) are plant secondary metabolites and have a similar chemical structure , size,
shape and charge to protein amino acids and can be mistakenly used in protein synthesis, interfere in biochemical
pathways, overstimulate receptors or chelate metal ions. The Consumption of a number of plants that contain NPAAs has been shown to have
acutely toxic effects in humans. The consumption of some seeds or vegetables that contain NPAAs inuences some people as a trigger for some
diseases or as an exacerbating factor. The effects of NPAAs on human health are not well understood. It has been observed that chimpanzees fed
alfalfa and also a volunteer subject who have intake alfalfa tablets have both developed a disease with all the characteristics of lupus
erythematosus ( an autoimmune disease) and by suppressing the consumption of alfalfa the disease disappears.
Most of NPAAs are of plant origin; these do not form part of the primary structure of proteins, they act as antimetabolites and most are found in
higher plants; they have the same basic structure as amino acids of animal origin. The substitution of a protein amino acid in protein synthesis
produces abnormal proteins which generate antibodies and modication of autoantigens as mechanism to break immunological tolerance and
trigger autoimmunity. Auto-antibodies formation is a characteristic of autoimmune disease. The toxic potential of NPAAs depend the amount
ingested and the consumption time. Chronic exposure to NPAAs could contribute to autoimmune disease development in genetically susceptible
individuals.
ABSTRACT
INDIAN JOURNAL OF APPLIED RESEARCH
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Volume - 11 | Issue - 03 | March - 2021 | . PRINT ISSN No 2249 - 555X | DOI : 10.36106/ijar
KEYWORDS : Non protein amino acids , plant toxin, autoimmune diseases
Briceida Lopez
Martinez
Clinical Laboratory. Hospital Infantil de Mexico “Federico Gomez” Mexico city.
Israel Parra
Ortega
Clinical Laboratory. Hospital Infantil de Mexico “Federico Gomez” Mexico city.
2
INDIAN JOURNAL OF APPLIED RESEARCH
dsDNA antibodies. After stopping the consumption of tablets, all the
patients were asymptomatic.
L-canavanine works as a potent antagonist that exhibits antimetabolic
activity in many living fungi as well as in animals by being
incorporated in the cell nucleus and other proteins and interfering
with DNA and RNA synthesis (11, 12). Animal experiments have
shown a number of deleterious effects following consumption of
legumes containing canavanine; so has been observed a signicant
reduction in plasma concentration of plasma arginine, lysine and
histidine (13). Prolonged consumption of alfalfa seeds by humans has
been associated with pancytopenia, anemia, leukopenia and the
development of antinuclear antibodies, attributed to canavanine in the
seeds ( 9 ).
Mechanisms of toxicity of NPAAs
The rst mechanism of toxicity identied for NPAAs was their ability
to replace a protein amino acid in protein synthesis resulting in the
synthesis of abnormal or nonnative protein. It has been shown that
there are a linear correlation between the concentration of the NPAA
and the level of incorporation into protein ( (14). The replacement of a
protein amino acid by an NPAA resembles a mutation (missence), in
which the replacement of a single base in DNA encodes another
protein amino acid in the polypeptide chain.
The typical toxic mechanism of NPAAs is that they function as mimic
of 20 protein amino acids and are mistakenly incorporated in proteins
in the place of the corresponding protein amino acids similar in
structure, thereby leading to the production of unnatural proteins that
cannot function properly. It is the case with azetidine-2-carboxilic
acid found in Canavalia majalis (Liliaceae) which is a mimic of
proline and a legume toxin canavanine that occurs in the seeds of jack
bean, canavalia ensiformis and Dioclea megacarpa in very high
concentrations (up to 6 and 10% respectively), which is a mimic of
arginine (15).
Interference in metabolic pathways
The L-arginine analogue, L-canavanine is synthesized by over 350
species of Papilionoideae including jack beans (canavalia ensiformis),
vine (Dioclea megacarpa) and wild potato (Hedysarum)alpinum).
Concentrations can reach up to 13% of the dry weight of seeds; It is a
very close structural analogue of L-arginine and serves as a substrate in
virtually every enzyme-mediated reaction that employs L-arginine. In
the rat L-canavanine is converted by arginase into urea and L-canaline
toxin. Arginine participates in the urea cycle, in the formation of
connective tissue and the synthesis of polyamines by the action of
arginase producing ornithine and this with ornithine-descarboxilase
(ODC) becomes putrescine (16,17).
Canavanine is an arginine antagonist, able to manifest antimetabolic
effects in viruses, bacteria and fungi as well as in animals by being
incorporated in the cell nucleus and proteins interfering with DNA and
RNA synthesis (11,18). In macrophages and polymorphonuclear
leucocytes, canavanine is able of prevent L-arginine derived synthesis
of nitric oxide (12). On the other hand has been shown than canavanine
cause a marked reduction in RNA synthesis in Escherichia coli
and also to decrease DNA synthesis in herpes virus. Canavanine has an
isoelectric point of 8.1 which decreases the basicity of histones which
are rich in arginine. This alters the function of DNA and decreases the
synthesis of histones, which has been demonstrated in mice, hamsters,
also in mon key kid ney cells. L-canav anine s upplied in hig h
concentration is lethal in rats and caused the death of an subject who
feeds on wild potatoes with a high content of canavanine ( 7 ). When
was administered in rats canavanine marked with radio isotopes; it was
observed that the amount of canavanine that is incorporated in the
proteins is equal to the amount of arginine (19).
Amino acids of Lathyrus
Several species of genus lathyrus are of economic importance; L
odoratus (sweet pea) and L. latifolius (everlasting pea) are
cultivated as ornamentals, while others such as L sativus, L.
cicero and L. clymenum are sources of food for humans and domestic
animals; these last three species have been implicated as causes of
neurological disorders in both humans and animals. In addition to the
genus Lathyrus , the genus Vicia also has 15 species that are
lathyrogens, among them Vicia faba. The disease known as lathyrism,
really is about two different diseases also produced by two different
substances; one that affects the central nervous system causing
neurolathyrism which is an irreversible paralytic disease and the other
is osteolathyrism in which bone and connective tissue problems
appear. A study of the free amino acids and related compounds in the
seeds of 49 species of lathyrus were found two NPAAs. While
working on an experimentally induced connective tissue disease, has
been observed that β-aminopropio-nitrile (BAPN) an NPAA found in
leguminous plant lathyrus; produced disastrous results in the test
animals; this compound it inhibited the cross-linking of collagen;
therefore was discovered that BAPN increased the solubility of
collagen such as bone collagen which had been hitherto unavailable
for study without prior denaturation. A lathyrogenic compound was
dened as any compound which induced an increase in the connective
tissue fragility and in collagen solubility in the 14-days-old-chick
embryo. L-2-4-Diaminobutanoico acid (2-4-DABA) is a NPAA
present in seeds of many species of lathyrus when injected into the
peritoneum of rats, caused liver damage and neurotoxicity.
Lathyrus sativus ( grass pea) is found in Europe, North America,
Asia, East Africa, Ethiopia and South America; it is used as food in
Spain in the form of porridge , contains various NPAAs; it is known as
almorta, alverjón and pea; its toxic effects appear when consumed over
a period of several weeks or months due to the presence of the
compound β-N-Oxalil-L-αβ-diaminopropionic acid (β-ODAP). L
sativus is the most widely cultivated species of Lathyrus and a valuable
source of food and fodder in some of the poorest regions of the world.
The best documented plant derived NPAA is B-ODAP produced by the
legum e lathyru s sativus . Prolong ed cons um pt ion r esults in
deg ene rative changes in the majo r cent ral ne rvous pathway
responsible for regulation of skeletal muscle function. The initial
effects of B-ODAP include cramping and weakness in the muscles of
the legs and can be reversible; however prolonged exposure leads to
irreversible damage and permanent central motor system decits.
B-ODAP may be regarded as a structural analogue of glutamic acid,
acts as a neuroexciting to central nervous system neurons and is
sel ect ive fo r glutama te rec ept ors. B -OD AP i nhi bits t yro sine
aminotransferase, which catalyzes the reaction between tyrosine
and 2 -o xo gl utarate to yield gl ut am at e an d the ketoacid
corresponding to tyrosine; B-ODAPs stimulates neural protein
kinase C and causes mitochondrial dysfunction (20). 4-glutamil-3-
aminopropio-nitrile is the toxin responsible for osteolathyrism since
it preventing the formation of crosslinks in collagen and elastin
which results in weak muscles and collagen disorders (collagen
diseases), also produces fragility of the blood capillary walls.
L-2-4-diaminobutiric acid, L-2,4-diaminobutanoic acid (DABA).
DABA was isolated from L. latifolius and shown to be acutely
neurotoxic to rats. This amino acid is a homologue of ornithine.
Induces ammonia toxicity (and hence neurotoxicity) in rats by
inhibiting the liver enzyme ornithine transcarbamylase. DABA may
cross the blood-brain barrier, in rats and other animals, using the
cationic amino acid transporter system and once introduced into the
brain, DABA acts as an anticonvulsant.
Sweet pea (peas or lodges) these seeds containing β-oxalylamino-L-
alanine (BOAA) that alters the synthesis of collagen; inhibits the
formation of collagen brils by the enzyme lysyl-oxidase,
preventing the formation of hydroxylysine. In rats fed a diet of 50%
sweet pea developed enlarged adrenals relative to control animals. The
main effect is on the formation of collagen brils. Symptoms are
similar to those of scurvy and copper deciency, which share the
common feature of inhibiting proper formation of collagen brils.
Β-N-(ϒ-Glutamyl)-aminopropionitrile(ϒ-glutamil-BAPN) was
isolated originally from seeds of L odoratus and L pusillus. The
physiologically acve part of the molecule is the BAPN moiety.
Both BAPN and ϒ-glutamyl-BAPN exercise their effects by inhibiting
the formation of cross-linkages between the polypeptide chains during
the synthesis of collagen. These seeds in animals produce aneurysm of
the aorta; this is similar a condition that occurs in humans (aneurysm of
the aorta).
β-L-Cyanoalanine (BCNA). Seeds of L savus and Vicia sava their
seeds contain significant concentraons of BCNA and even higher
amounts of the ϒ-glutamil derivave. Administraon of BCNA by
stomach tube to weanling male rats at a concentraon of 15 mg per
100g bod y we ight produced reversible hyperactivit y, tremors,
Volume - 11 | Issue - 03 | March - 2021 | . PRINT ISSN No 2249 - 555X | DOI : 10.36106/ijar
convulsions and rigidity. BCNA inhibits cystathionase in the
pyrid oxal-5-phosphate-requiring conversion of cistathionine to
cyst eine an d also the activity of aspartate dec arboxyl ase. In
mammalian liver this is the major pathway by which cysteine is
synthesized from methionine, which is an essential amino acid.
Mimosine
Mimosine was isolated from Mimosa púdica but its present in high
concentrations in the leaves and seeds of leucaena leucocephala
containing as much as 8-10% dry weight of mimosine, while even
higher concentrations can occur in the seeds. It is an analogue of
tyrosine. Mimosine (hydroxyphenylalanine) present in seeds, stem
and leaves is an inhibitor of DNA replication; inhibits various
metal-containing enzymes involved in the synthesis of DNA, purines
and thymidines; it also induces apoptosis of leukemic cells due to
damage to the mitochondria (21).
The ingestion of leaves and seeds of leucaena has been held
responsible for the loss of hair in both animals and humans. It is also
found in guajes that in Mexico are used for human consumption due
to their high protein content; it is a powerful chelating agent it
kidnapping copper, iron, zinc and magnesium therefore it inhibits the
enzymes responsible for the synthesis of DNA (ribonucleotide
reductase). It is also a substrate for phenyl-alanyl-RNA synthetase and
can replace tyrosine as a substrate for the enzyme tyrosinase.
Mimosine inhibits a number of enzymes, such as dopamine β-
hydroxylase and tyrosinase. Dopamine-β-hydroxylase was inhibited
because of the removal of Cu by the strong chelating properties of the
amino acid. Mimosine also reduces the synthesis of dopamine and
serotonine, furthermore it is an inhibitor of pyridoxal phosphate,
transaminases, tyrosine-decarboxylase, cystathionine synthetase and
cystathiona se. In addition to its potent metal-chelating ability
(including Cu, Zn and Fe) (22-23)).
Indospicine an analogue of arginine, which is found in several
members of the genera indigofera a leguminous native of Africa and
Asia and which is a potent antimetabolite of arginine. The indigofera
plant has a high protein content and is considered very useful because it
tolerates droughts , oods and salinity; has 1.5% of the amino
acid. Indospicine inhibits, but is not hydrolyzed by arginase, also
inhibits the incorporation of arginine and consequently other amino
acids, into liver protein. Indospicine is a competitive inhibitor of
arginase and causes both liver degeneration and abortion. As an
arginine analogue indospicine has the potential to interfere with a
range of mammalian arginine metabolic pathways, as arginine is a
precursor for the synthesis not only of protein but also of nitric oxide,
urea, polyamines, proline, glutamate, creatine and agmatine(24).
Many species of Indigofera contain a second toxic amino acid,
canavanine is also produced, plus a third toxin β-nitropropionic
acid, which is a “suicide inhibitor” of succinate dehydrogenase. Camel
or horse meat contaminate with indospicine readily killed dogs but
spared camels and horses that had fed on indospicine-containing
plants.
Mucuna pruriens (velvet bean). Other NPAA is 3-4-dihydroxy-
phenylalanine (L-DOPA) which is found in high concentrations (6-
9%) in mucuma seeds; which is able to replace the protein amino acid
tyrosine in protein synthesis, the catechol group on the L-DOPA
molecule allows it to interact strongly with divalent metals affecting
tyrosinase activity (25).
L-homoarginine. which is present in Lathyrus cicero and Lathyrus
sativus differs from L-arginine only in that it contains an additional
backbone methylene group (CH3) and can replace L-arginine in
mam mal s i n most physi olo gic al pro cesses. Hom oargin ine is
recognized as a normal metabolite in humans. L-arginine and L-
homoarginine compete as a substrate of nitric oxide synthase. This
amino acid was a substrate for rat liver arginase (26). This enzyme
catalyze the hydrolysis of homoarginine to yield urea and lysine, the
latter being an essential diet requirement for animal species. Also
can be formed homocitrulline in tissue in several types of reactions.
Antibodies directed against proteins that contain homocitrulline have
been found in rheumatoid arthritis patients sera. More recently, it has
been shown that homocitrulline-containing proteins are present in
rheumatoid arthritis (27). Homoarginine induces hypersensitivity
and mortality in rats when administered intraperitoneally at
10mmol/Kg body weight. When homoarginine was fed to rats on a
lysine-decient diet food intake and growth rate were both reduced.
The seeds of Lens culinaris (lentils), also contain homoarginine, have
been not observed adverse effects in human. Homoarginine is an
uncompetitive inhibitor of human liver and bone alkaline phosphatase,
but is not active against the intestinal and placental forms of the
enzyme.
l-homoarginine, which is present in lathyrus cicero, lathyrus sativus
and lens culinaris (lentils), can replace L-arginine in mammals in most
physiological process. L-homoarginine inhibits bacterial growth.
Missincorporation into protein in humans since it is an endogenous
amino acid synthesized in the kidneys, also can decrease the
production of nitric oxide by endothelial cells where it is an important
determinant of vascular tone and blood pressure (28).
AZETIDINE-2-CARBOXYLIC ACID (AZE)
Aze is ubiquitously present in low concentrations in vegetation, which
kidnapping metals from the soil and transfer then to various parts of
the plants. In certain species, aze accumulates to exceedingly high
levels notably in the bulbous roots of table beets and sugar beets (beta
vulgaris) up to 5%. Thus, aze is present in the food chain in small
concentrations in vegetables. However it is in high concentrations in
certain foods, especially in dairy products derived from livestock
fed sugar beet by products ( 15 ).The worldwide prevalence of multiple
sclerosis (MS) has been linked to beet agriculture (Beta vulgaris).
Beets contain Aze which can replace proline in proteins leading to
neurodegeneration and autoimmune disorders. There is a possibility
that aze present in beet a potent cell toxin, implicated in MS, can enter
the human feed chain (2).
Multiple sclerosis is considered as an autoimmune disease; attack the
central nervous system. Epidemiologists have seen an increased
pattern of MS cases in countries located farther from the equator.
People of northern European descent are at highest risk of developing
MS. Rubenstein (15) proposed that aze replaces L-proline residues in
myelin basic protein (MBP) of the myelin sheath. Aze is the lower
homolog of proline that is identical to proline except in that it contains
four instead of ve members in its ring . Aze is highly toxic to many
organisms because it is incorrectly incorporated into proteins instead
of proline modifying the three dimensional structure of proteins
incl udin g collag en, kera tin and hemo globin. A link was also
established between the geography of beet agriculture and the
worldwide prevalence of MS. In addition, MS is a relatively modern
disease and correlates with the increase in cultivation of beets for sugar
which now accounts for around 30% of the world supply of sucrose.
Aze which is present in a number of plants including Convallaria
majalis (lily of the valley),some liliaceae and Beta vulgaris (sugar
beets) readily replaces L-proline in protein synthesis. Aze was shown
to inhibit the uptake of 14C-proline by E coli and inhibit proline
biosynthesis from glutamate through feedback inhibition. This
feedback inhibition has also been demonstrated by analogues of the
aromatic amino acids: phenylalanine, tyrosine and tryptophan.
Canavanine
L-canavanine is synthesized by over 350 species of leguminous plant
including jack beans ( Canavalia ensiformis ), vine ( Dioclea
megacarpa ) and wild potato ( Hedysarum alpinum ).
L-canavanine serves as a substrate in virtually every enzymes
mediated reaction that employs L-arginine. In the rat L-canavanine is
converted by arginase into urea and the toxin L-canaline. L-
canavanine is also a substrate for inducible nitric oxide synthase;
the enzyme that converts L-arginine in nitric oxide; a potent
vasodilator and inhibition of platelet activation (7).
Canavanine is found in many species of the Papilionoideae, which is a
sub-family of the Leguminosae. Seeds are a particularly rich source of
this amino acid and concentrations as high as 13% dry weight has
been reported in those of Dioclea megacarpa. Canavanine is
incorporated into mammalian protein in competition with arginine
because the arginyl-tRNA synthetase is unable to differentiate between
arginine and canavanine. It is signicant that macaques fed on the
seeds and sprouts of Medicago sativa (alfalfa), which contain
canavanine, develop hematological and serological abnormalities
(28). These abnormalities are similar those seen in human SLE, an
autoimmune disease that adversely affects the kidney and skin. SLE
can be induced in apparently normal subjects that are fed leguminous
which contain L-canavanine. ( 29 )
Canavanine can affect B-cell function, accelerating the disease in
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Volume - 11 | Issue - 03 | March - 2021 | . PRINT ISSN No 2249 - 555X | DOI : 10.36106/ijar
autoimmune mice and inducing antibody-mediated autoimmune
phenomena on normal mice. Canavanine also affects the charged
surface membrane properties of autoimmune B-cells.; such alterations
may be associated with an abnormal (auto) immune response. L-
canaline is formed by the hydrolysis of canavanine ( a reaction
catalyzed by arginase) which is an importan factor in the toxicity of
canavanine (30).
L-canavanine is a substrate for arginyl tRNA synthetase and replace l-
arginine during protein synthesis; this substitution can occur in every
arginine -contai ning protei ns and res ults in the pro duction of
structurally aberrant canavanyl proteins (31). Arginine constitutes 8%
of amino acids in the human collagen. The result is a disruption of
enzymatic activity and a rapid degradation of the protein. L-
canavanine is a less basic molecule than l-arginine; the pK of the
guanidooxi group is 7.04 vs 12.48 of the guanido group in l-arginine
and this can impact the function and structure of the protein and the
health and function of the organism. Substitution of a protein amino
acid for a NPAA has similarities a missense mutation in which
substitution of a single base in DNA will encode another protein amino
acid in the polypeptide chain.
The toxicity of L-canavanine in animals has been well documented;
has been observed cases of poisoning among cattle allowed to forage
on jack beans, Canavalia ensiformis; the seeds of which contain
approximately 2.5% L-canavanine by dry weight. Several studies of
feeding trials that showed L-canavanine sulfate induced toxic effects
in mice. All mice fed L-canavanine at a concentration of 2.0 g/kg
mouse died within 24 hours. Also has been reported hematologic
and serologic abnormalities similar to those observed in human (32).
Sword beans (canavalia gladiata) are one of many underutilized but
exceptionally productive, large-seeded tropical leguminous. This
leguminous is consumed in Srilanka, southern India, Indonesia as
a substitute for mashed potatoes; In Guatemala as a coffee substitute
and other 79Central American countries. Sword beans are not
commonly used as a food; the reason is the presence of antinutritional
factors such as haemagglutinins, tannins, phytates and canavanine 4% (7).
The existence of the genetic component in SLE is based mainly on
family aggregation and high concordance in twins monozygotes; it is
estimated that the prevalence of SLE in relatives is 66 times higher
than in general population. This frequency of the disease is due to the
fact they live in the same house and eat the same foods. On the
other hand leguminous are consumed since childhood and it has been
observed that canavanine accumulates in the human organism causing
illness in some people when they consume them for a long time (33).
Vicia faba.Broad beans contain vicin and convicin that are hydrolyzed
in the digestive tract by the action of β-glucosidase, giving divicin and
isouracil. Beans, broad beans and soy produce methane causing
intestinal cramps and atulence. The beans in large quantities produce
agglutination of erythrocytes causing small clots that decrease the
uidity in the blood capillaries. Favism is a genetic disease. People
with a deciency of the enzyme glucose-6-dehydrogenase have
hemolytic problems due to the ingestion of broad beans (Vicia fava)
and also decreases the concentration of glutathione due to the action of
the compounds known as vicin and convicin; which when hydrolyzed
in the digestive tract give rise to divicine and isouracil, which are
directly responsible for the disease. The gene that encode for the
enzyme is found on the X chromosome; therefore the disease is
more frequent in men than in women. The dihydroxyphenilalanine
found in broad beans and velved beans is also an agent of favism.
Broad beans also contains canavanine 1 g% in dry weight (5).
Lentils. Lentils also contain canavanine 1.0 g% dry weight and
homoarginine; furthermore contain several antinutrients such as
trypsin inhibitors, an enzyme that metabolizes phytic acid which binds
to iron and zinc minerals (5).
Autoimmune Diseases
Autoimmune diseases also called collagen diseases; these diseases
have three things In common; their etiologies remains unknown, the
prognosis is not hopeless, remain poor and the specicity of available
dru gs qu est io nable . S LE consi dered to be th e pro totyp e of
autoimmune disease in which the immune response is directed against
a wide variety of self-antigens resulting in damage to various organs
and systems. In chimpanzees feed alfalfa, they developed a disease
with all the characteristics of lupus erythematosus and on the other
hand a volunteer developed lupus erythematosus while ingesting
alfalfa seeds for a study of hypercholesterolemia. By suppressing
the consumption of alfalfa the disease disappeared both in the monkeys
and in the voluntary subject. Subsequently several cases of induction
or exacerbation of the disease due to the intake of alfalfa tablets were
reported. (8, 34). When was administered in rats canavanine marked
with radio isotopes it was observed that the amount of canavanine that
is incorporated in the proteins is equal to the amount of arginine ( 18 ).
This fact causes the loss of positive charge of arginine and therefore
the interactions of the amino acids with its neighbors are
modied; therefore immune system can attack the canavanine
proteins, leading to autoimmune diseases such as rheumatoid arthritis,
MS, psoriatic arthritis, SLE, and Sjogrens syndrome. Anti-DNA
antibodies were found in the blood serum of chimpanzees and rats fed
alfalfa. Canavanine has an isoelectric point of 7.1 wherever arginine
its isoelectric point is 12.48 which decreases basicity in proteins that
are rich in arginine. The proline used in the production of collagen is
synthesized from arginine and in the rst reaction participates the
arginase enzyme producing ornithine. Proline is hydroxylated by
prolyl hydroxylase enzyme to hydroxyproline which stabilizes the
collagen. On the other hand has been observed that when prolyl-
hy dr oxyla se e nz ym e is i nh ibi te d, c ol lagen los s it s na ti ve
conguration. The nal step of collagen synthesis consists of cross-
link formation by the enzyme lysyl-oxidase whose two cofactors are
copper and pyridoxal-phosphate; this gives the bril the strength to
perform its major tensile role. This enzyme when is inhibited by
canaline , (a metabolite of canavanine), then synthesis of collagen
is disturbed and on the other hand antibodies are generated. The
lysyl-oxidase enzyme is also inhibited by BAPN a NPAA present in
lathyrus sativus, this blocks the activity of the enzyme by kidnapping
copper. The tensile effects decreased due to this fact that
interlinked links are diminished. Collagen is distributed in all the
organs of the human body and the skin; due to this fact there are
injuries throughout the body during the disease. For this reason the
autoimmune diseases also are known as collagen diseases (35).
SLE can be induced in apparently normal subjects that are fed
leguminous which contain NPAAs. The toxic potential of these
NPAAs depend on the amount ingested and the time of consumption.
Canavanine is the NPAA more studied; when this amino acid is
metabolized by the arginase enzyme, canaline is produced which
inhibits metabolism of ornithine, decreasing the production of several
compound necessary for cell division and growth. On the other hand
protein synthe sis is disturb an d autoa ntibodies are produc ed
generating immune complexes which inducing the autoimmune
disease. Canavanine disturb the collagen synthesis; others NPPAs
inhibit the activity of several enzymes and others such as BAPN found
in sweet bean (lathyrus odoratus), specically inhibits the formation
of cross-linking of collagen and elastin chains. This legume in addition
contain canavanine (5); is added to rice and consumed frequently
worldwide; furthermore there are other legumes such as alfalfa, lentils,
soy bean, common bean, that also contain canavanine. See Table 1.
Furthermore, in seeds of various lathyrus species several toxic amino
acids have been fou nd such as hom oarginine, mimo sine, and
indospicine in seeds, sprouts and all parts of the leguminous plant.
Table 1. Plant Derived Non-protein Amino Acids, Source(s),
Known Protein Amino Acid Analogues And What Their Effects
4
INDIAN JOURNAL OF APPLIED RESEARCH
Volume - 11 | Issue - 03 | March - 2021 | . PRINT ISSN No 2249 - 555X | DOI : 10.36106/ijar
Source
amino acid or
derivates
action or
disease
Alfalfa
L-Canavanine
cytotoxic
Mucuma
pruriens
3-4-
hidroxifenilalanina
favism
Canavalia
ensiformis
L-canavanine
cytotoxic
Dioclea
megacarpa
L-canavanine
cytotoxic
Lathyrus cicero
Homoarginine
cytotoxic
Lathyrus
α-γ- diaminobutyric
acid
latyrogenic
Brassica
glucosinolate
goitrogenic
Leucaena glauca
Mimosine
goitrogemic
Lathyrus sativus
β-
aminopropionitrile
osteolathyrogen
Lathyrus
odoratus
β-diamino propionic
acid
osteolathyrogen
It has been shown that a lower concentrations of NPAAs, there is a
linear correlation between the concentration of the NPAA and the level
of incorporation into protein which can produce changes in the protein
affecting its tertiary structure and its function. The immune system can
attack these proteins, leading to autoimmune diseases such as
rheumatoid arthritis, MS, psoriatic arthritis, SLE, Sjogrens syndrome,
scleroderma, dermatomyositis, also in cells with Alzheimer´s disease
(36). This demonstrates the need for additional studies on NPPAAs to
support the diagnosis of some diseases.
This information suggests that majority of patients with some
autoimmune disease have consumed some leguminous plant that
contain canavanine (see table 2), homoarginine or other NPAA que
disturb t he synt he si s of coll ag en and in du ce formation of
autoantibodies.
Table 2. Legume Plants Containing L-canavanine And Their
Family To Which They Belong
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INDIAN JOURNAL OF APPLIED RESEARCH
5
Volume - 11 | Issue - 03 | March - 2021 | . PRINT ISSN No 2249 - 555X | DOI : 10.36106/ijar
Convallaria
majalis
azetidine-2-
carboxilic acid
multiple
sclerosis
Indigofera
spicata
indospicine
hepatotoxic
Beta vulgaris
azetidine-2-
carboxilic acid
multiple
sclerosis
PLANT
COMMON NAME
FAMILIA
Albizia julibrissin
acacia
fabáceae
Canavalia ensiformis
Jack bean
fabáceae
Canavalia gladiata
sword beans
fabaceae
Canavalia majalis
sable bean
fabáceae
Cicer arietinum
chickpea
fabaceae
Dioclea megacarpa
fabaceae
Hedysarum alpinum
wild potatoes
fabaceae
Indigofera tintorea
creeping indigo
fabaceae
Lathyrus odoratus
sweet pea
Fabaceae
Lathyrus sativus
grass pea
fabaceae
Lens culinaris
lentils
fabaceae
Leucaena leucocephala
guaje
fabaceae
Medicago sativa
alfalfa
fabaceae
Vicia fava
broad bean
fabaceae
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