Inositol Metabolism
Carbohydrate Metabolism

Author: Gianpiero Pescarmona
Date: 18/01/2008


Inositol, (of which the most prominent naturally-occurring form is myo-inositol, cis-1,2,3,5-trans-4,6-cyclohexanehexol), is a carbocyclic polyol that plays an important role as the structural basis for a number of secondary messengers in eukaryotic cells (Kegg Pathways)

Inositol endogenous synthesis (Kegg Pathways)

Myo-Inositol is synthesized from glucose-6-phosphate (G-6-P) in two steps. First, G-6-P is isomerised by INYNA1 to myo-inositol 1-phosphate, which is then dephosphorylated by IMPA1 to give myo-inositol.

The synthesis of inositol requires oxidized nicotinamide adenine dinucleotide (NAD) and was stimulated by NH4C1 and MgC12. NADH inhibits the reaction. Phosphorylated inositol accumulated in the absence of MgC12, suggesting that inositol-phosphate is an intermediate in the pathway and that Mg ions stimulate the dephosphorylation of inositol-phosphate.

The limiting step in the Inositol synthesis is INYNA1 (INO1_HUMAN) that has a *GLU/GLN = 1.66

Inositol uptake from the diet

Uptake is a Na+-dependent process and it is inhibited by high glucose (20 mM).

myo-Inositol Phosphates synthesis

inositol phosphates during cell cycle 2007


The proapoptotic factors Bax and Bak regulate T Cell proliferation through control of endoplasmic reticulum Ca(2+) homeostasis.


Myo-inositol to chiro-inositol conversion

myo-Inositol oxygenase (MIOX) catalyses the first committed step in the only pathway of myo-inositol catabolism, which occurs predominantly in the kidney . The enzyme is a non-haem-iron enzyme that catalyses the ring cleavage of myo-inositol with the incorporation of a single atom of oxygen.

Myo-Inositol oxygenase: molecular cloning and expression of a unique enzyme that oxidizes myo-inositol and D-chiro-inositol, 2001

Risk factors for hepatic encephalopathy in patients with cirrhosis and refractory ascites: relevance of serum sodium concentration. 2010

  • Hyponatraemia is common in patients with advanced cirrhosis and is associated with remarkable changes in brain cells, particularly a reduction in myoinositol and other intracellular organic osmolytes related to the hypo-osmolality of the extracellular fluid. It has been recently suggested that hyponatraemia may be an important factor associated with the development of overt hepatic encephalopathy (HE). To test this hypothesis, we retrospectively analysed the incidence and predictive factors of overt HE using a database of 70 patients with cirrhosis included in a prospective study comparing transjugular intrahepatic portosystemic shunts (TIPS) vs large-volume paracentesis in the management of refractory of ascites. Variables used in the analysis included age, sex, previous history of HE, treatment assignment (TIPS vs large volume paracentesis plus albumin), treatment with diuretics, serum bilirubin, serum creatinine and serum sodium concentration. Laboratory parameters were measured at entry, at 1 month and every 3 months during follow-up and at the time of development of HE in patients who developed this complication. During a mean follow-up of 10 months, 50 patients (71%) developed 117 episodes of HE. In the whole population of patients, the occurrence of HE was independently associated with serum hyponatraemia, serum bilirubin and serum creatinine. In conclusion, in patients with refractory ascites, the occurrence of HE is related to the impairment of liver and renal function and presence of hyponatraemia.

Subclinical hepatic encephalopathy: proton MR spectroscopic abnormalities. 1994

MATERIALS AND METHODS In a double-blind study, overt hepatic encephalopathy (HE) and SCHE (defined with clinical and neuropsychiatric tests) were compared by means of H-1 MR spectroscopic criteria--reduction in cerebral myo-inositol (< 2 standard deviations [SDs] from normal) and choline (< 2 SDs from normal) with or without increased cerebral glutamine (> 1 SD from normal)--in 20 patients with cirrhosis.

Cerebral abnormalities in patients with cirrhosis detected by proton magnetic resonance spectroscopy and magnetic resonance imaging. 1997

Myoinositol/creatine ratios in gray (.36 +/- .17) and white (.35 +/- .22) matter voxel were reduced significantly (P < .0001) in cirrhotic patients compared with healthy volunteers (gray matter, .51 +/- .11; white matter, .64 +/- .16).

Core Canonical Pathways Involved in Developing Human Glioblastoma Multiforme (GBM). 2017

  • Abstract
    Glioblastoma multiforme (GBM) is the most common and aggressive type of the primary brain tumors with pathologic hallmarks of necrosis and vascular proliferation. The diagnosis of GBM is currently mostly based on histological examination of brain tumor tissues, after radiological characterization and surgical biopsy. The ability to characterize tumors comprehensively at the molecular level raises the possibility that diagnosis can be made based on molecular profiling with or without histological examination, rather than solely on histological phenotype. The development of novel genomic and proteomic techniques will foster in the identification of such diagnostic and prognostic molecular markers. We analyzed the global differential gene expression of a GBM cell line HTB15 in comparison to normal human Astrocytes, and established a few canonical pathways that are important in determining the molecular mechanisms of cancer using global gene expression microarray, coupled with the Ingenuity Pathway Analysis (IPA®). Overall, we revealed a discrete gene expression profile in the experimental model that resembled progression of GBM cancer. The canonical pathway analysis showed the involvement of genes that differentially expressed in such a disease condition that included Inositol pathway, Polo like kinases, nNOS signaling, and Tetrapyrrole biosynthesis. Our findings established that the gene expression pattern of this dreaded brain cancer will probably help the cancer research community by finding out newer therapeutic strategies to combat this dreaded cancer type that leads to the identification of high-risk population in this category, with almost hundred percent mortality rate.
    More Tetrapyrrole less heme?
  • Tetrapyrrole biosynthesis and increased accumulation is a characteristic of malignant cells(13–16). Therapeutic strategies have developed in targeting cancer cells by photodynamic therapy and killing these malignant cells by blocking tetrapyrrole biosynthesis and irreversible damage to the mitochondria where these reactions mostly occurs(ref). IPA analysis showed pathway of increased biosynthesis of tetrapyrrole compounds in GBM cells in contrast to normal Astrocytes (Figure 4).

inositol and MTHFR

Endoplasmic reticulum stress increases the expression of methylenetetrahydrofolate reductase through the IRE1 transducer. 2008
inositol induces MTHFR



Hepatic heme and drug metabolism in rats with chronic mountain sickness. 1986

  • Rats chronically exposed to hypobaric conditions develop pulmonary hypertension, right heart failure, hemoglobinemia, and in preliminary studies were recently found to have increased hepatic cytochrome P-450 content and activity of heme oxygenase, the rate-limiting enzyme for heme breakdown. To further delineate effects of chronic hypoxic, hypobaric exposure, on hepatic physiology and biochemistry, we have studied heme and drug metabolism in male Sprague-Dawley rats exposed to hypoxic conditions for 4-5 wk. Hypoxia, produced by exposure of rats to room air under hypobaric conditions (approximately 380 Torr), caused marked polycythemia [hematocrit (Hct) 70% vs. control Hct 43%], plasma hemoglobinemia, depletion of plasma haptoglobin, and decreased hemopexin concentrations. It also led to significant (20-30%) increases in concentrations of total hepatic heme and microsomal cytochrome P-450 and increased activities of heme oxygenase. In contrast, activity of 5-aminolevulinate synthase, the rate-limiting enzyme of hepatic heme synthesis, was significantly decreased in hypoxic rats and was not as inducible as in control normoxic rats. Hypoxia did not alter the rest of the heme synthetic pathway, as shown by a normal rate of conversion of 5-aminolevulinate to heme. Hypoxic exposure had no effect on the concentration of hepatic cytochrome-b5 but decreased activity of NADPH-cytochrome c reductase. Rates of metabolism of aminopyrine, benzphetamine, ethoxyresorufin, and warfarin were similar in hepatic microsomes obtained from hypoxic and normoxic rats. Thus the oxygen-requiring processes of hepatic heme and drug metabolism were well maintained despite chronic profound hypoxia sufficient to cause cardiopulmonary complications.
AddThis Social Bookmark Button