European Review for Medical and Pharmacological Sciences 2011; 15: 931-936 Inositol safety: clinical evidences G. CARLOMAGNO, V. UNFER AGUNCO Obstetrics & Gynecology Center, Rome (Italy) Abstract. – Myo-inositol is a six carbon ent required by the human cells for the growth cyclitol that contains five equatorial and one axi- and survival in the culture. In humans and other al hydroxyl groups. Myo-inositol has been classi- species, Myo-inositol can be converted to either fied as an insulin sensitizing agent and it is L- or D-chiro-inositol by epimerases. Early stud- commonly used in the treatment of the Polycys- tic Ovary Syndrome (PCOS). However, despite ies showed that inositol urinary clearance was al- its wide clinical use, there is still scarce informa- tered in type 2 diabetes patients, the next step tion on the myo-inositol safety and/or side ef- was to link impaired inositol clearance with in- fects. The aim of the present review was to sum- sulin resistance (for a review see1). Because of marize and discuss available data on the myo-in- these properties, inositol have been classified as ositol safety both in non-clinical and clinical set- “insulin sensitizing agent”2. tings. The main outcome was that only the highest In the recent years, inositol has found more dose of myo-inositol (12 g/day) induced mild and more space in the reproductive clinical prac- gastrointestinal side effects such as nausea, fla- tice3-6. Indeed, since the main therapy for Poly- tus and diarrhea. The severity of side effects did cystic Ovary Syndrome (PCOS) is the use of in- not increase with the dosage. sulin sensitizing agent inositol is mainly use as a chronic treatment for this disease2,5,7,8. Further- Key Words: more, recently it was proposed as a preventing Myo-inositol, PCOS, Side effects, Dosage, NTDs. agent for folate-resistant neural tube defects (NTDs)9,10. The toxicity of Myo-inositol has not been di- rectly investigated. However, a number of studies have been conducted to investigate the efficacy of myo-inositol in preventing the pathological Introduction changes associated with experimental dia- betes11,12 (and other pathology models) and as a Myo-inositol (also known as inositol, hexahy- cancer chemoprevention agent13-16. The data of droxycyclohexane, or cis-1,2,3,5-trans-4,6-cyclo- these studies provide useful data for evaluating hexanehexol) is a six carbon cyclitol that con- the toxicity of myo-inositol. The relevant studies tains five equatorial hydroxyl groups and one in will be described and discussed hereafter. axial position. The main source of myo-inositol With the present review we aim to summarize is the diet, indeed it is found in a wide variety of some data that are availed in the literature in both foods such as whole grains, seeds, and fruits. non clinical and clinical settings. Myo-inositol can also be synthesized from glu- cose, the immediate precursor being fructose 6- Non Clinical Studies phosphate, which is converted to myo-inositol by Pugliese et al11 investigated the potential effect a cyclase. Myo-inositol is a precursor in the of myo-inositol on diabetes-induced vascular phosphatidylinositol cycle. It is a source of sever- functional changes. Myo-inositol was adminis- al second messengers including diacylgycerol, tered to diabetic rats as supplement in the diet, which regulates some members of the protein ki- ranging from 0.5, 1, or 2% (w/w). Vascular func- nase C family, inositol-1,4,5-triphosphate, which tional changes were evaluated by examining: (1) modifies intracellular calcium levels, and phos- 131I-labeled bovine serum albumin (BSA) perme- phatidylinositol-3,4,5-biphosphate, which is in- ation of vessels in multiple tissues, (2) glomeru- volved in the signal transduction. It is a compo- lar filtration rate (GFR), estimated as renal plas- nent of cell membranes and is an essential nutri- ma clearance of 57Co-labeled EDTA, (3) regional Corresponding Author: Gianfranco Carlomagno, Ph.D.; e-mail: [email protected] 931 G. Carlomagno, V. Unfer blood flows, measured with 15-microns 85Sr-la- chemical changes triggered by kainate-induced beled microspheres, and 4) endogenous albumin status epilepticus (SE) in rats. The effects of and IgG urinary excretion rates, quantified by ra- myo-inositol were investigated after both acute dial immunodiffusion assay. After 1 month of in- (1 day) and sub-acute (28 days) administration. duced-diabetes, 131I-BSA tissue clearance in- For the acute administration the study was per- creased significantly (2- to 4-fold) in the anterior formed on three different groups, (1) male Wistar uvea, choroid-sclera, retina, sciatic nerve, aorta, rats received intraperitoneal injection of kainic new granulation tissue, diaphragm, and kidney acid (10 mg/kg). Six hours following the treat- but was unchanged in skin, forelimb muscle, and ment, rats received myo-inositol 30 mg/kg, by in- heart. Myo-inositol-supplemented diets reduced jection; (2) rats received only 30 mg/kg myo-in- diabetes-induced increases in 131I-BSA clearance ositol (by injection); (3) rats treated with only (in a dose-dependent manner) in all tissues. saline as controls. However, only in new granulation tissue and di- For the sub-acute study also three different aphragm did the 2% myo-inositol diet complete- groups were analysed (1) rats were treated on ly normalize vascular albumin permeation. Dia- day 1 with kainate received twice a day myo-in- betes-induced increases in GFR and in urinary ositol for 28 days; (2) rats were not treated with albumin and IgG excretion were also substantial- kainate on day 1 and received myo-inositol for ly reduced or normalized by dietary myo-inositol 28 days; (3) rats were not treated with kainate supplements. Increased blood flow in anterior and received saline instead of myo-inositol as uvea, choroid-sclera, kidney, new granulation tis- controls. Changes in proteins expression in the sue, and skeletal muscle in streptozotocin-D hippocampus and neocortex, were evaluated. (STZ-D) rats also was substantially reduced or Proteins studied were: GLUR1, subunit of gluta- normalized by the 2% myo-inositol diet. Notably, mate receptors, calcium/calmodulin-dependent the Authors noted that myo-inositol had minimal protein kinase II (CaMKII); and heat shock pro- if any effects on the above parameters in control tein 90. No changes were found in the acute ex- rats. periments. However, on 28th day of experiment Coppey et al12 studied whether administration the amounts of GLUR1 and CaMKII were of myo-inositol could prevent the detrimental strongly reduced in the hippocampus of KA changes of motor nerve conduction velocity, en- treated animals but MI significantly halted this doneurial blood flow and endothelium-dependent reduction. Notably, in the group that received vascular relaxation of arterioles induced by ex- myo-inositol alone didn’t show change in the perimental diabetes animal model. Diabetic male amounts of studies proteins. rats of 8-9 weeks old were fed with 1% by weight of myo-inositol as a dietary supplement Chronic Studies and Carcinogenesis for a period of about 8 weeks. Administration of Liao et al18 studied the effects of myo-inositol myo-inositol completely reversed the decrease in and hexaphosphate inositol (HI) on the carcino- intracellular myo-inositol content caused by ex- genesis associated to ulcerative colitis (UC) in a perimental diabetes. Treating diabetic rats with newly developed mouse model. Female C57BL/6 myo-inositol improved the reduction of en- mice were subjected to long-term, cyclic dextran doneural blood flow and motor nerve conduction sulphate sodium (DSS) treatment and fed a 2- velocity and prevented the metabolic derange- fold iron-enriched diet. In this long-term study of ments associated with either activation of the chronic UC and associated colorectal carcino- polyol pathway or increased non-enzymatic gly- genesis, mice were randomized into six groups. cation. Myo-inositol treatment did not prevent Group 1, Group 2 and Group 3 were adminis- the gross signs of diabetes-associated toxicity, tered water, 1% inositol and 1% HI, respectively, such as decrease in body weight change, increase in the drinking water throughout the experiment in blood glucose or serum free fatty acids (FFA) as negative controls (n = 5 mice per group). and triglycerides (TG). In the myo-inositol Group 4, Group 5 and Group 6 mice were sub- group, the values of these parameters were the jected to cyclic DSS treatment. Group 4 received same as the in the diabetic untreated group. This no further treatment (positive control), whereas clearly shows that myo-inositol did cause no fur- groups 5 and 6 mice were administered 1% myo- ther functional impairment in diabetic rats. inositol or 1% HI, respectively in the drinking Solomonia et al17 investigated whether treat- fluid. The study lasted 255 days. Myo-inositol ment with myo-inositol could influence the bio- and HI did not induce any change in body weight 932 Inositol safety: clinical evidences or food consumption, both in DSS-treated and the above parameters in control or diabetic rats. untreated mice. In mice not treated with DSS, However, retinal capillary basement membrane myo-inositol or HI did not induce any change in width (CBMW) was increased significantly (ap- body weight, food consumption or mortality, as proximately 50% versus controls) after 9 months compared to negative controls receiving water. of diabetes and in the control group myo-inositol No colorectal tumors were found in mice receiv- increased CBMW to the level of untreated dia- ing Myo-inositol of HI. The colons of these mice betic rats (myo-inositol had no effect on CBMW were morphologically normal. Myo-inositol 1% in each diabetic group). The number of retinal caused a significant reduction of tumour frequen- capillaries containing pericyte nuclei and peri- cy, tumour multiplicity and tumour volume.