This ppt gives you an idea of Citrulline-a naturally occuring basic amino acid, its structure, its role as marker, its uses, its clinical importance,etc.

1. By
Dr.Arun Babu.N.B.
II year, MD (Biochemistry)
V.M.K.V. Medical College

2.  Named after Citrullus vulgaris (Water-melon)
 Accumulates CIT as it’s the only way
for the specific decomposition of
free OH- radical.
 Citrulline is a very potent scavenger
of the hydroxyl radical.

3.  2-Amino-5-(carbamoylamino) pentanoic acid – IUPAC
 Most reactive moiety in CIT – α amino group.
 α carbon – oxidatively converted to aldehyde after
releasing amino & carboxyl groups of CIT.

4.  Naturally occuring basic amino acid
 Not a constituent of protein due to lack of codons
 Key intermediate in biosynthesis of Arginine & in Urea
cycle
 Neither present in Tissue proteins, nor in blood
 Present in high concn. in human brain
 Also present in milk.
 Formed in Mitochondria Leaves to Cytoplasm (further
reactions of urea cycle occur)
 FMN, FAD, Heme & THB – cofactors for ARGCIT.

5.  Intestinal epithelium converts Glutamine  Citrulline
 Intestinal epithelium is the only tissue that expresses an ATP
dependent glutamate reductase necessary for this conversion.

6. Ornithine depletion INHIBITS urea synthesis.
Ornithine Replenishment – completely dependent on source
of ARG
Urea synthesis in Liver – Dependent on Citrulline (gut) &
Arginine (kidney).
ARG – used by many cells to produce NO.

7.  Windmueller & Spaeth showed that there is a continuous
release of CIT from small intestine  circulation.
 They also showed that CIT is an end-product of Glutamine
metabolism
 CIT – synthesized from ARG in intestine (Arginase and
Ornithine Carbamoyl Transferase are present in enterocytes)
 Action of 2 enzymes that catabolise CIT is very low in
intestine [Arginosuccinate synthase (ASS) & Arginosuccinate
lyase (ASL)]

8.  A marker of Renal Failure
 A marker of Intestinal Failure
 A Nutritional Therapeutic
 Treating Muscle weakness/ Fatigue/ Dementia/ Sickle
cell disease
 For Body building
 To increase energy
 To increase athletic performance
 To decrease high BP in children after heart surgery
 To open up veins & arteries to improve blood flow

9.  Kidneys-Main organs metabolizing CIT (ASS & ASL
expressed along the tubules)
 To establish relation between Citrullinemia & Renal
insufficiency, a study was done on rats subjected to
Nephrectomy(NX) [10%-90%]
Plasma CIT – Increased in mild renal failure (10 to 33% of NX)
No change in Uremia 2 well known markers of
No changes in Creatininemia Uremic states.

10.  Another study to find a marker for onset of Renal failure –
to study time course of changes in aminoacidemia (Rats
36% NX, 1-21days)
 Uremia Peaked 24 – 48 hrs after NX
 Creatininemia
 Creatinine Clearance – Decreased concomitantly
 All the above 3markers,
Returned to control values in the next few days
Increased only during the last 2 weeks
 Plasma CIT concentration
Increased 2x , 48 hrs after NX
Remained at high level for the next 20 days

11.  In humans,
Plasma CIT concentration – Increased according to the
progression of renal failure.
Good correlation exists between CIT & plasma concentration
of Creatinine.

12.  Small intestine – only significant source of circulating CIT
 In short bowel syndrome (SBS) patients, post-absorptive
plasma CIT Valuable biomarker in the diagnosis and
outcome of intestinal failure.
 Plasma CIT- correlated to small bowel length & to net
digestive absorption of fat
 Is a marker of functional absorptive bowel length
 Plasma CIT has got:
High Sensitivity
High Specificity
High Positive Predictive Value

13.  Another study confirmed validity of CIT as a marker of small
intestinal enterocyte mass & absorption function in SBS
patients.
 Serum CIT levels in SBS patients correlated well with:
- Remnant Small Bowel Length
- Surface Area
- Digestive protein absorption
- Intestinal Absorption
 Another study showed, serum CIT levels in SBS infants
correlated linearly with:
- Bowel length
- Tolerance to calorie intake
- Serum CIT >19μmol/L in children with SBS- associated with
development of enteral tolerance – may be a useful predictive test.

14. Stratification to associate citrullinemia to intestinal disease
< 10 μmol/L - Diffuse total villous atrophy
10 - 20 μmol/L- Proximal-only total villous atrophy
20 - 30 μmol/L- Partial villous atrophy
 CIT - used to quantify radiation induced epithelial loss.

15.  All conditions characterized by an impairment of the active
intestinal massHypocitrullinemia proportional to
severity of diseaseARG levels
 Low CIT production = Low de novo ARG synthesis.
 Hence extra ARG is to be made available to patients with
intestinal failure.[But ARG is taken up by liver & Arg
supplementation is unsafe in some situations because of its
role as NO precursor.]
 Providing CIT-Better way to fill Arg pools. Hence CIT
rather than Arg should be administered when intestinal
function is compromised.

16. In a study with rats (massive intestinal resection -80%):
 CIT supplementation – more effective than Arg
supplementation
 CIT content in liver-Did not vary with CIT supplementation
 CIT - accumulated in all other tissues
 CIT - passes freely through the liver
 ARG supplementation-Deleterious for Nitrogen balance
 CIT – had positive effect on the intestinal adaptation in
terms of intestinal mucosa weight & protein content
 CIT- aslo able to limit the body weight loss associated with
SBS.
 Administering an amino acid that escapes splanchnic
extraction, it’s possible to deliver a more adequate amount
of nitrogen to peripheral tissues.

17.  In a study using old malnourished rats in which an
impaired response to renutrition had been proven,:
- Increased muscle protein content (+20%, p<0.05)
- Stimulating protein synthesis (+90%, p<0.05)
 CIT supplementation lead to dramatic improvement of:
- Nitrogen balance
- Protein status

18.  INDIRECT
Related to its ability to generate ARG
Related to its ability to stimulate Insulin secretion
Related to its ability to stimulate GH secretion
 DIRECT
By stimulating protein synthesis

19.  So far, only 1 amino acid (LEUCINE) was proven to have a
direct effect on muscle protein synthesis. For this action, the
availability of other essential aa along with high insulinemia
is necessary (i.e., post-prandialsituation).
 CIT-synthesized & released by intestine mainly in case of
low protein intake or post-absorptive state.

20.  Working Hypothesis
LEU & CIT – 2 essential aa in controlling the nitrogen
balance & muscle protein composition, depending on
nutritional state.
 Conclusion
LEU&CIT- play same function, but in different physiologic
conditions
LEU- Allows for optimal utilization of dietary aa by
stimulating post-prandial protein synthesis
CIT- Allows for preservation of the muscle proteins &
maintains minimal protein synthesis in post-absorptive state.
LEU- Not metabolized in liver (lack of Transaminases)
With regard to Liver metabolism,
LEU is not metabolized ; CIT is not taken up.

21.  Auto antibodies like Anti perinuclear factor (APF), Anti
keratin antibodies (AKA), Anti cyclic citrullinated peptide
(Anti-CCP) antibodies – Specifically associated with RA.
 In patients with RA, APF & AKA specifically bind to
substrates containing modified amino acid-CIT.
 A peptide-based ELISA –developed using citrullinated
cyclic peptide substrates for detection of anti-CCP & it may
be used as a functional replacement of immunofluorescence
tests used for detection of APF & AKA.

22.  To detect acute & chronic renal failure
 To estimate the degree of renal damage
 As a specific marker of normal functioning of PCT
 As a marker of extent & severity of villous atrophy in
coeliac disease
 As a marker for acute cellular rejection in small intestinal
transplant recepients.
 As a marker of functional absorptive bowel length
 Anti-CCP antibody
Important serological marker for diagnosis of RA
Prognostic marker for development of erosive disease

23. TYPE I
 Arginosuccinate Synthase def.
 Autosomal Recessive
 Lethargy progressing to coma
 Mental Retardation
 Hyperammonemia
TYPE II
 Defect in mitochondrial aspartate
/glutamate carrier(CTLN2)
 Autosomal Recessive
 Neonatal Intrahepatic Cholestasis
 Adult- Sudden behavioral changes
 Hyperammonemia
 Stupor
 Coma

24. Clinical Features
 Lethargy
 Hypothermia
 Hyperammonemia
 Lethargy
 Apnea
 Brain Oedema
 Coma
 Seizure
 Vomiting
 Mental Retardation
Treatment
 Low protein diet
 Arginine Supplementation
 Breast Milk to be avoided, as
it contains Citrulline.
High Blood levels of Ammonia & Citrulline
High Urine levels of Orotate & Citrulline
Citrullinuria (1-2g/day)

25. 1. Lippincott’s Biochemistry – 5th Edn
2. Harper’s Illustrated Biochemistry- 29th Edn
3. Stryer’s Biochemistry-7th Edn
4. Devlin’s Textbook of Biochemistry-7th Edn
5. Lehninger’s Principles of biochemistry-5th Edn
6. Harrison’s Principles of Internal Medicine-17th edn
7. Christopher Moinard, Luc Cynober; “Citrulline- A new
player in the control of nitrogen homeostasis”; The Journal of
Nutrition, 6th Amino acid assessment workshop.