Changes in serum and urinary myo-inositol levels in chronic glomerulonephritis

Inositols and metabolic disorders: From farm to bedside

Inositol and its derivates are catching interest in metabolism since taking part in several physiological processes, including endocrine modulation. Through several mechanisms mostly mediated by insulin signaling, these compounds regulate the activities of several hormones and are essential in oocytes maturation. It is interesting to point out the contribution of an inositol deficiency in the development of several diseases, mainly in the metabolic and endocrine setting. Inositols derive from both diet and endogenous production; among causes of inositol deficiency reduced dietary intake, increased catabolism and/or excretion, decreased biosynthesis, inhibition of gut and cellular uptake and altered microbiota could be considered. Mounting direct and indirect evidence suggests that the two main isoforms (Myo-inositol-inositol, D-chiro-inositol) are implied in glycemic and lipidic metabolism and supplementation yield a beneficial effect on these parameters without hazards for health. Moreover, they have a role in polycystic ovary syndrome, acting as insulin-sensitizing agents and free radical scavengers, helping to regulate metabolism and promoting ovulation. The aim of this narrative review is to discuss the role of inositols in metabolic function disorders paying attention to whether these compounds could be efficacious and safe as a therapeutic agent with a focus on dietary intake and the role of gut microbiota.

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Inositol deficiency is implicated in the development of metabolic and endocrine diseases.

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Inositol compounds could be safe food supplement to restore metabolic imbalance.

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Inositol compounds partly derive from microbiota phytases entering in bacterial metabolism.

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Diet inositol content has a role in shaping gut microbiota and the host metabolism.

Simple and non-invasive screening method for diabetes based on myoinositol levels in urine samples collected at home

OBJECTIVE

To establish a simple screening method for diabetes based on myoinositol (MI) in urine samples collected at home.

RESEARCH DESIGN AND METHODS

Initially, we evaluated the stability of urinary MI (UMI) at room temperature (RT; 25°C) and 37°C in 10 outpatients with type 2 diabetes. We then enrolled 115 volunteers without a current or history of diabetes. In all subjects, glucose intolerance was diagnosed by 75 g oral glucose tolerance test (75gOGTT). To assess the association between UMI or urine glucose (UG) and plasma glucose (PG), urine samples were also collected at 0 and 2 hours during 75gOGTT. All the subjects collected urine samples at home before and 2 hours after consuming the commercially available test meal. UMI levels at wake-up time (UMI_wake-up), before (UMI_premeal) and 2 hours after the test meal (UMI_{2h-postprandial}) were measured using an enzymatic method. ΔUMI was defined as UMI_{2h-postprandial} minus UMI_premeal.

RESULTS

Differing from UG, UMI was stable at RT and 37°C. UMI was increased linearly along with an increase in PG, and no threshold for UMI was observed. UMI was closely associated with blood glucose parameters obtained from a 75gOGTT and hemoglobin A1c (HbA1c) at hospital after adjustment for age, sex, body mass index and serum creatinine. UMI_wake-up, UMI_premeal, UMI_{2h-postprandial} and ΔUMI at home were higher in diabetic subjects than non-diabetic subjects even after the above adjustment. Receiver operating characteristics curve (ROC) analyses revealed that for the screening of diabetes, the area under the curve for ROC for UMI_{2h-postprandial} and ΔUMI (0.83 and 0.82, respectively) were not inferior to that for HbA1c ≥48 mmol/mol, which is the American Diabetes Association (ADA) criteria for diabetes.

CONCLUSIONS

MI measurement in urine samples collected at home before and after the meal would be a simple, non-invasive and valuable screening method for diabetes.

Metabolomic biomarkers are associated with mortality in patients with cirrhosis caused by primary biliary cholangitis or primary sclerosing cholangitis

Aim:

To assess the ability of signature metabolites alone, or in combination with the model for end-stage liver disease-Na (MELD-Na) score to predict mortality in patients with cirrhosis caused by primary biliary cholangitis or primary sclerosing cholangitis.

Materials & methods:

Plasma metabolites were detected using ultrahigh-performance liquid chromatography/tandem mass spectrometry in 39 patients with cirrhosis caused by primary biliary cholangitis or primary sclerosing cholangitis. Mortality was predicted using Cox proportional hazards regression and time-dependent receiver operating characteristic curve analyses.

Results:

The top five metabolites with significantly greater accuracy than the MELD-Na score (area under the receiver operating characteristic curve [AUROC] = 0.7591) to predict 1-year mortality were myo-inositol (AUROC = 0.9537), N-acetylputrescine (AUROC = 0.9018), trans-aconitate (AUROC = 0.8880), erythronate (AUROC = 0.8345) and N6-carbamoylthreonyladenosine (AUROC = 0.8055). Several combined MELD-Na-metabolite models increased the accuracy of predicted 1-year mortality substantially (AUROC increased from 0.7591 up to 0.9392).

Conclusion:

Plasma metabolites have the potential to enhance the accuracy of mortality predictions, minimize underestimates of mortality in patients with cirrhosis and low MELD-Na scores, and promote equitable allocation of donor livers.

To receive a liver transplant, patients with cirrhosis need to be listed on the US liver transplant waiting list based on a score called the model for end-stage liver disease-Na (MELD-Na) score that is expected to accurately rank the patients based on urgency for a liver transplant. However, MELD-Na score is not sufficiently accurate to identify many patients with cirrhosis with the highest urgency, and this results in longer waiting times on the liver transplant list, and therefore higher death rates. We identified several metabolomic biomarkers that can increase the accuracy of the MELD-Na score, and optimize the allocation of donor livers for transplantation of patients with cirrhosis.

Urinary myo-inositol is associated with the clinical outcome in focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) and minimal change disease (MCD) have similar initial histological findings; however, their prognoses are distinct. Therefore, it is of great importance to discriminate FSGS from MCD in the early phase of disease and predict clinical prognosis. A discovery set of 184 urine samples (61 healthy control, 80 MCD, and 43 FSGS) and a validation set of 61 urine samples (12 healthy control, 26 MCD, and 23 FSGS) were collected at the time of kidney biopsy. Metabolic profiles were examined using nuclear magnetic resonance spectroscopy. Of 70 urinary metabolites, myo-inositol was significantly higher in FSGS patients than in control patients (discovery set, 2.34-fold, P < 0.001; validation set, 2.35-fold, P = 0.008) and MCD patients (discovery set, 2.48-fold, P = 0.002; validation set, 1.69-fold, P = 0.042). Myo-inositol showed an inverse relationship with the initial estimated glomerular filtration rate (eGFR) and was associated with the plasma level of soluble urokinase-type plasminogen activator receptor in FSGS patients. Myo-inositol treatment ameliorated the decreased expression of ZO-1 and synaptopodin in an in vitro FSGS model, and as myo-inositol increased, myo-inositol oxygenase tissue expression decreased proportionally to eGFR. Furthermore, urinary myo-inositol exhibited an increase in the power to discriminate FSGS patients, and its addition could better predict the response to initial treatment. In conclusion, urinary myo-inositol may be an important indicator in the diagnosis and treatment of FSGS patients.

Unique metabolomic signature associated with hepatorenal dysfunction and mortality in cirrhosis

The application of nontargeted metabolomic profiling has recently become a powerful noninvasive tool to discover new clinical biomarkers. This study aimed to identify metabolic pathways that could be exploited for prognostic and therapeutic purposes in hepatorenal dysfunction in cirrhosis. One hundred three subjects with cirrhosis had glomerular filtration rate (GFR) measured using iothalamate plasma clearance, and were followed until death, transplantation, or the last encounter. Concomitantly, plasma metabolomic profiling was performed using ultrahigh performance liquid chromatography-tandem mass spectrometry to identify preliminary metabolomic biomarker candidates. Among the 1028 metabolites identified, 34 were significantly increased in subjects with high liver and kidney disease severity compared with those with low liver and kidney disease severity. The highest average fold-change (2.39) was for 4-acetamidobutanoate. Metabolite-based enriched pathways were significantly associated with the identified metabolomic signature (P values ranged from 2.07E-06 to 0.02919). Ascorbate and aldarate metabolism, methylation, and glucuronidation were among the most significant protein-based enriched pathways associated with this metabolomic signature (P values ranged from 1.09E-18 to 7.61E-05). Erythronate had the highest association with measured GFR (R-square = 0.571, P <0.0001). Erythronate (R = 0.594, P <0.0001) and N6-carbamoylthreonyladenosine (R = 0.591, P <0.0001) showed stronger associations with measured GFR compared with creatinine (R = 0.588, P <0.0001) even after controlling for age, gender, and race. The 5 most significant metabolites that predicted mortality independent of kidney disease and demographics were S-adenosylhomocysteine (P = 0.0003), glucuronate (P = 0.0006), trans-aconitate (P = 0.0018), 3-ureidopropionate (P = 0.0021), and 3-(4-hydroxyphenyl)lactate (P = 0.0047). A unique metabolomic signature associated with hepatorenal dysfunction in cirrhosis was identified for further investigations that provide potentially important mechanistic insights into cirrhosis-altered metabolism.

Nutritional and Acquired Deficiencies in Inositol Bioavailability. Correlations with Metabolic Disorders

Communities eating a western-like diet, rich in fat, sugar and significantly deprived of fibers, share a relevant increased risk of both metabolic and cancerous diseases. Even more remarkable is that a low-fiber diet lacks some key components-as phytates and inositols-for which a mechanistic link has been clearly established in the pathogenesis of both cancer and metabolic illness. Reduced bioavailability of inositol in living organisms could arise from reduced food supply or from metabolism deregulation. Inositol deregulation has been found in a number of conditions mechanistically and epidemiologically associated to high-glucose diets or altered glucose metabolism. Indeed, high glucose levels hinder inositol availability by increasing its degradation and by inhibiting both myo-Ins biosynthesis and absorption. These underappreciated mechanisms may likely account for acquired, metabolic deficiency in inositol bioavailability.

Polycystic Ovary Syndrome: Insights into the Therapeutic Approach with Inositols

Polycystic ovary syndrome (PCOS) is characterized by hormonal abnormalities that cause menstrual irregularity and reduce ovulation rate and fertility, associated to insulin resistance. Myo-inositol (cis-1,2,3,5-trans-4,6-cyclohexanehexol, MI) and D-chiro-inositol (cis-1,2,4-trans-3,5,6-cyclohexanehexol, DCI) represent promising treatments for PCOS, having shown some therapeutic benefits without substantial side effects. Because the use of inositols for treating PCOS is widespread, a deep understanding of this treatment option is needed, both in terms of potential mechanisms and efficacy. This review summarizes the current knowledge on the biological effects of MI and DCI and the results obtained from relevant intervention studies with inositols in PCOS. Based on the published results, both MI and DCI represent potential valid therapeutic approaches for the treatment of insulin resistance and its associated metabolic and reproductive disorders, such as those occurring in women affected by PCOS. Furthermore, the combination MI/DCI seems also effective and might be even superior to either inositol species alone. However, based on available data, a particular MI:DCI ratio to be administered to PCOS patients cannot be established. Further studies are then necessary to understand the real contents of MI or DCI uptaken by the ovary following oral administration in order to identify optimal doses and/or combination ratios.

Pharmacodynamics and pharmacokinetics of inositol(s) in health and disease

INTRODUCTION

Inositol and its derivatives comprise a huge field of biology. Myo-inositol is not only a prominent component of membrane-incorporated phosphatidylinositol, but participates in its free form, with its isomers or its phosphate derivatives, to a multitude of cellular processes, including ion channel permeability, metabolic homeostasis, mRNA export and translation, cytoskeleton remodeling, stress response.

AREAS COVERED

Bioavailability, safety, uptake and metabolism of inositol is discussed emphasizing the complexity of interconnected pathways leading to phosphoinositides, inositol phosphates and more complex molecules, like glycosyl-phosphatidylinositols.

EXPERT OPINION

Besides being a structural element, myo-inositol exerts unexpected functions, mostly unknown. However, several reports indicate that inositol plays a key role during phenotypic transitions and developmental phases. Furthermore, dysfunctions in the regulation of inositol metabolism have been implicated in several chronic diseases. Clinical trials using inositol in pharmacological doses provide amazing results in the management of gynecological diseases, respiratory stress syndrome, Alzheimer's disease, metabolic syndrome, and cancer, for which conventional treatments are disappointing. However, despite the widespread studies carried out to identify inositol-based effects, no comprehensive understanding of inositol-based mechanisms has been achieved. An integrated metabolomics-genomic study to identify the cellular fate of therapeutically administered myo-inositol and its genomic/enzymatic targets is urgently warranted.

The utility of urinary myo-inositol as a marker of glucose intolerance

OBJECTIVE

The most common screening tests for glucose intolerance are fasting plasma glucose (FPG) and glycated hemoglobin (HbA1c). Because it reflects the current status of hyperglycemia, urinary myo-inositol (UMI) may be useful. We evaluated UMI as a screening tool for glucose intolerance.

DESIGN AND METHODS

A cross-sectional, community-based population study of 1057 Japanese residents. 173 with an FPG level between 5.5 and 6.9 mmol/L and an HbA1c under 6.5% had an oral glucose tolerance test. We measured UMI level before (fasting UMI) and 2h after (2h-UMI) glucose ingestion. Δ-UMI was defined as the difference between fasting UMI and 2h-UMI.

RESULTS

Δ-UMI, 2h-UMI and HbA1c levels significantly increased as glucose intolerance worsened. Δ-UMI level was significantly positively correlated with 2h-UMI level (r=0.896, p<0.001). Using cutoff levels from receiver operating characteristic (ROC) analyses, the sensitivity of Δ-UMI (82.1%) and 2h-UMI (79.3%) were higher than that of HbA1c (48.3%). The area under the ROC curve values for Δ-UMI (0.903) and 2h-UMI (0.891) were higher than that for HbA1c (0.785).

CONCLUSIONS

2h-UMI is useful as a non-invasive screening of glucose intolerance.

The development of a sensitive myo-inositol analyser using a liquid chromatograph with a post-label fluorescence detector

A sensitive liquid chromatographic analysis for myo-inositol was developed using glycocyamine as the post-labelling reagent. The sensitivity was 500 pmol/injection. The system was applied to analyse myo-inositol in sera from eight patients with chronic renal failure. The average concentration of serum myo-inositol was 498.6 +/- 257.0 mumol/L before haemodialysis, and 244.0 +/- 131.1 mumol/L after haemodialysis. These results indicated that the kidney is the main site of myo-inositol metabolism.

Phosphoinositide metabolism in a polyoma-BK-virus-transformed pancreatic islet cell line: evidence for constitutively activated phospholipase C

We have characterized the phosphoinositide metabolism in a polyoma-BK-virus-transformed rat pancreatic islet cell line which has highly malignant characteristics, expresses viral T-antigen and has lost insulin-secreting capacity. After incorporation with [3H]inositol to isotopic equilibrium, all inositol metabolites were analyzed. When compared with normal pancreatic islets, increased levels of inositol 1,4,5-trisphosphate (Ins-1,4,5-P3), inositol 1,3,4-trisphosphates and inositol tetrakisphosphate (Ins-P4), and decreased levels of phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP2) were found. The Ins-1,4,5-P3/PIP2 ratio increased, whereas the PIP2/PIP ratio was not altered after the transformation. In the pancreatic islet cell line there was a stable accumulation of inositol phosphates at 3.3 mM glucose. Glucose, KCl, cholecystokinin (CCK) and carbachol with and without LiCl were all without effect on the accumulation of inositol phosphates. Somatostatin inhibited the accumulation of inositol phosphates but a Ca(2+)-free/EDTA solution did not. Preincubation with cholera toxin or pertussis toxin inhibited the accumulation of inositol phosphates at 3.3 mM glucose except for Ins-P4, whereas no effect was observed on the phosphoinositides. NaF stimulated the accumulation of inositol phosphates, with a concomitant decrease in the phosphoinositides, whereas neomycin was without effect on the inositol phosphates. In normal pancreatic islets, pertussis toxin inhibited the CCK-induced increase in Ins-1,4,5-P3, whereas no effect was seen at 3.3 mM glucose. Finally, pertussis toxin inhibited the CCK-induced increase in the Ins-1,4,5-P3/PIP2 ratio in normal pancreatic islets. The same inhibition was also found in the pancreatic islet cell line at 3.3 mM glucose. We conclude that in the transformed pancreatic islet cell line the phosphoinositide hydrolysis is constitutively activated at the level of phospholipase C, with a substantial loss of regulatory control.

Enzymatic assay of myo-inositol in serum

An enzymatic spectrophotometric method for determination of myo-inositol in serum is described. The method is sensitive and rapid to perform without special equipment. Linearity between the amount of myo-inositol and absorbance was obtained in the range of 0.5 to 3 nmol myo-inositol per assay. The amounts of myo-inositol determined in sera from apparently healthy subjects agree well with gas chromatographic data.

Effects of pre- and postweaning undernutrition on polyphosphoinositide pools in rat kidney

The effects of undernutrition on polyphosphoinositide levels in rat kidneys removed and frozen immediately after animal death or 10 min later were determined. Weanling (21-day-old) rats of dams fed a 5 or 22% protein diet and litters fed either normal or protein-deficient diets for an additional six wk were used. Nutritional deprivation lowered phosphatidylinositol-4-phosphate (PtdIns4P) preferentially (35-40%) but preserved phosphatidylinositol-4,5-bisphosphate (PtdIns4,5P2) at weaning. This effect was not completely reversed in animals nutritionally rehabilitated after weaning. Postweaning protein deficiency did not reduce the levels of these lipids. Postmortem loss was the same for all five groups, minimal for PtdIns4P and about one-third for PtdIns4,5P2.

The nutritional significance, metabolism, and function of myo-inositol and phosphatidylinositol in health and disease

Recent advances in nutritional and biochemical research have substantiated the importance of inositol as a dietary and cellular constituent. The processes involved in the metabolism of inositol and its derivatives in mammalian tissues have been characterized both in vivo and at the enzyme level. Biochemical functions elucidated for phosphatidylinositol in biological membranes include the mediation of cellular responses to external stimuli, nerve transmission, and the regulation of enzyme activity through specific interactions with various proteins. Inositol deficiency in animals has been shown to produce an accumulation of triglyceride in liver, intestinal lipodystrophy, and other abnormalities. The metabolic mechanisms giving rise to these latter phenomena have been extensively studied as a function of dietary inositol. Altered metabolism of inositol has been documented in patients with diabetes mellitus, chronic renal failure, galactosemia, and multiple sclerosis. A moderate increase in plasma and nerve inositol levels by dietary supplementation has been suggested as a means of treating diabetic neuropathy, although excessively high levels, such as are found in uremic patients, may be neurotoxic. A thorough consideration of the biochemical functions of inositol and a further characterization of various diseases with the aid of appropriate animal models may suggest a possible role for inositol and other dietary components in their prevention and treatment

The conversion of D-xylose into D-threitol in patients without liver disease and in patients with portal liver cirrhosis

An oral D-xylose tolerance test was carried out on 12 patients with portal liver cirrhosis, on 7 patients with active fatty liver disease and on 29 subjects without liver diseases. D-Xylose and D-threitol were measured by means of gas-liquid chromatography. Fifteen percent of the D-xylose dose excreted in urine within five hours was recovered as D-threitol. The proportion of D-threitol was greater when the collection was extended to 24 h. The D-threitol excretion was markedly diminished in cirrhotic patients, suggesting that a substantial proportion of the D-xylose-D-threitol conversion occurs in the liver. No decrease was detected in patients with fatty liver disease. No significant change in D-xylose excretion was observed in liver cirrhosis or in fatty liver disease. D-Threitol can be regarded as the main end product of D-xylose metabolism in man. The role of the glucuronate pathway in the D-xylose-D-threitol conversion is discussed.