Hiroaki Akai

Oxidative damage to mitochondrial DNA and its relationship to diabetic complications

Increased oxidative stress induced by hyperglycemia may contribute to the pathogenesis of diabetic complications. Oxidative stress is known to increase the conversion of deoxyguanosine (dG) to 8-hydroxydeoxyguanosine (8-OHdG) in DNA, which is linked to increased mitochondrial DNA (mtDNA) deletions. We investigated mtDNA deletions and 8-OHdG in the muscle DNA of non-insulin-dependent diabetes mellitus (NIDDM) patients. mtDNA deletion of 4977 bp (delta mtDNA4977) and the content of 8-OHdG in the muscle DNA of the NIDDM patients were much higher than those of the control subjects. There was a significant correlation between delta mtDNA4977 and the 8-OHdG content (P < 0.0001). Both delta mtDNA4977 and the 8-OHdG content were also correlated with the duration of diabetes. Delta mtDNA4977 and the 8-OHdG content in muscle DNA increased in proportion to the severity of diabetic nephropathy and retinopathy. This is the first report that an increase in delta mtDNA4977 and 8-OHdG is proportional to the severity of diabetic complications. Oxidative mtDNA damage is speculated to contribute to the pathogenesis of diabetic complications though a defect in mitochondrial oxidative phosphorylation or other mechanisms. 8-OHdG and delta mtDNA4977 are useful markers to evaluate oxidative mtDNA damage in the diabetic patients.

The effects of coenzyme Q10 treatment on maternally inherited diabetes mellitus and deafness, and mitochondrial DNA 3243 (A to G) mutation

Summary The characteristic clinical features of diabetes mellitus with mitochondrial DNA (mtDNA) 3243(A-G) mutation are progressive insulin secretory defect, neurosensory deafness and maternal inheritance, referred to as maternally inherited diabetes mellitus and deafness (MIDD). A treatment for MIDD to improve insulin secretory defects and reduce deafness has not been established. The effects of coenzyme Q10 (CoQ10) treatment on insulin secretory response, hearing capacity and clinical symptoms of MIDD were investigated. 28 MIDD patients (CoQ10-DM), 7 mutant subjects with impaired glucose tolerance (IGT), and 15 mutant subjects with normal glucose tolerance (NGT) were treated daily with oral administration of 150 mg of CoQ10 for 3 years. Insulin secretory response, blood lactate after exercise, hearing capacity and other laboratory examinations were investigated every year. In the same way we evaluated 16 MIDD patients (control-DM), 5 mutant IGT and 5 mutant NGT subjects in yearly examinations. The insulin secretory response assessed by glucagon-induced C-peptide secretion and 24 h urinary C-peptide excretion after 3 years in the CoQ10-DM group was significantly higher than that in the control-DM group. CoQ10 therapy prevented progressive hearing loss and improved blood lactate after exercise in the MIDD patients. CoQ10 treatment did not affect the diabetic complications or other clinical symptoms of MIDD patients. CoQ10 treatment did not affect the insulin secretory capacity of the mutant IGT and NGT subjects. There were no side effects during therapy. This is the first report demonstrating the therapeutic usefulness of CoQ10 on MIDD. [Diabetologia (1998) 41: 584–588]

Urinary chiro-Inositol Excretion is an Index Marker of Insulin Sensitivity in Japanese Type II Diabetes

OBJECTIVE To determine the relationship between urinary chiro-inositol excretion and insulin sensitivity in Japanese type II diabetic patients. RESEARCH DESIGN AND METHODS Eighteen subjects were age-matched, nonobese, type II diabetic patients. Eight subjects had impaired glucose tolerance (IGT), and 10 had normal glucose tolerance (NGT). We quantified urinary chiro-inositol excretion using gas chromatography-mass spectrometry and the insulin sensitivity index (SI), and glucose effectiveness (SG) using Bergmans modified minimal model method. RESULTS The urinary excretion of chiro-inositol was much lower in the diabetic patients (32.3 ± 16.0 μmol/day, means ± SD) than in the NGT subjects (96.0 ± 17.6; P < 0.0001) and IGT subjects (58.9 ± 11.6; P < 0.0001). SI was much lower in the diabetic patients (3.81 ± 1.49) than in the NGT subjects 6.30 ± 1.59, P < 0.0005). SG was much lower in the diabetic patients (2.14 ± 0.56) than in the NGT subjects (3.07 ± 0.38, P < 0.0001). There was a significant correlation between urinary chiro-inositol excretion and SI (r = 0.766), as well as a significant correlation between urinary chiro-inositol excretion and SG (r = 0.747). CONCLUSIONS There is a direct relationship of urinary chiro-inositol excretion to insulin sensitivity and SG in humans. Urinary chiro-inositol excretion might be useful as a metabolic index of insulin sensitivity in type II diabetes.

Pancreatic beta-cell secretory defect associated with mitochondrial point mutation of the tRNALEU(UUR) gene: a study in seven families with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS)

SummaryRecent evidence suggests possible linkage between diabetes mellitus and mitochondrial gene mutation. We surveyed mitochondrial tRNALEU(UUR) (3243) mutation in 7 mitochondrial encephalomyopathy, lactic acidosis and stroke-like episode (MELAS) families and identified 24 mutated subjects (7 MELAS probands and 17 non-MELAS relatives) as well as 11 non-mutant family members. An OGTT in the 24 mutant relatives revealed 14 diabetic subjects, 3 with impaired glucose tolerance and 7 with normal glucose tolerance and all non-mutant family members as having normal glucose tolerance. Insulinogenic index was significantly reduced in the mutant diabetic subjects and those with impaired and normal glucose tolerance in comparison with the normal control subjects and the non-mutant members. Urinary 24-h C-peptide immunoreactivity excretion was markedly reduced in the mutant diabetic subjects and those with normal and impaired glucose tolerance, compared with the control subjects and the non-mutant family members. Plasma C-peptide immunoreactivity 6 min after glucagon injection was markedly reduced in the mutant diabetic subjects and those with normal and impaired glucose tolerance compared with the control subjects and the non-mutant family members. Si, an index of insulin sensitivity of the four mutant subjects was within normal range. Islet cell antibodies were negative in sera of eight mutated diabetic subjects, 2 and 6 with impaired and normal glucose tolerance, respectively. Diabetic retinopathy and nephropathy were demonstrated in 7 (50%) and 12 (85.7%) of 14 mutant diabetic subjects, respectively. Neurosensory deafness was demonstrated in 12 (85.7%) of 14 mutated diabetic subjects, (66.7%) of 3 mutated impaired glucose tolerant subjects, but not detected in 6 mutated normal glucose tolerant subjects and 11 non-mutant family members. These findings suggest that the tRNALEU(UUR) mutation is associated with pancreatic beta-cell secretory defect of insulin.

Diabetes With Mitochondrial Gene tRNALYS Mutation

OBJECTIVE To solve a possible relationship between mtDNA mutation of tRNALYS(8344) and diabetes, we have surveyed the tRNALYS mutation, glucose intolerance, and insulin secretory capacity in a Japanese family with diabetes and myoclonic epilepsy with ragged-red fiber disease. Several lines of evidence suggested possible linkage between mtDNA mutation and diabetes (1–4). RESEARCH DESIGN AND METHODS DNA was isolated from peripheral lymphocytes. The polymerase chain reaction analysis for the tRNALYS(8344) mutation of the mtDNA was conducted as described by Larsson (5). Insulin secretory capacity was assessed by 24-h urinary C-peptide immunoreactivity response (CPR) excretion and plasma CPR to glucagon administration. RESULTS We identified seven subjects with the tRNALYS mutation as well as seven non-mutated members in the pedigrees. Oral glucose tolerance tests in the pedigree indicated that five of the mutated subjects were diabetic, one had impaired glucose tolerance, and one had normal glucose tolerance (NGT), whereas all nonmutated family members had NGT. The pedigree shows maternal transmission of diabetes and the tRNALYS mutation over three generations. Twenty-four-hour urinary excretion of CPR was significantly reduced in the mutant subjects (mean ± SD, 67.8 ± 79.2 nmol/day, n = 6, P < 0.001) compared with the nonmutant members (276.6 ± 41.8 nmol/day, n = 5) and the age-matched normal control subjects (263 ± 64.3 nmol/day, n = 12). Plasma CPR 6 min after glucagon injection demonstrated a marked reduction in the mutant subjects (3.68 ± 3.45 nmol/l, n = 5, P < 0.001) compared with the nonmutant members (19.4 ± 1.17 nmol/l, n = 5) and the normal control subjects (15.8 ± 3.81 nmol/l, n = 12). Bilateral neurosensory deafness was demonstrated in five of seven (71.4%) mutant subjects (five of five [100%] mutated diabetic patients), but not detected in six nonmutant members. CONCLUSIONS This observation is the first report of association of diabetes with the mitochondrial tRNALYS mutation. Insulin secretory capacity was significantly lower in the mutant members than in the nonmutated members. These findings suggest that the pancreatic β-cell secretory defect of insulin might be one of the phenotypes of the mitochondrial tRNALYS mutation.

Effect of manidipine and delapril on insulin sensitivity in type 2 diabetic patients with essential hypertension

The open trial was designed to evaluate the effects of long-term antihypertensive treatment with the calcium-channel blocker, manidipine and the angiotensin converting enzyme (ACE) inhibitor, delapril on insulin sensitivity in Japanese non-insulin dependent diabetes mellitus (NIDDM) patients with essential hypertension. We measured the insulin sensitivity index (SI) and the glucose-effectiveness (SG) by the use of Bergmans minimal model method in 18 hypertensive NIDDM patients before and after administration of manidipine (group A) or delapril (group B) for 3 months. Manidipine treatment for 3 months significantly improved SI in group A from 3.35 +/- 0.61 (x 10(-4) min-1 microU-1 ml-1) to 4.70 +/- 1.34 (P < 0.05). Delapril treatment for 3 months also significantly improved SI in group B from 3.56 +/- 1.04 to 5.00 +/- 0.87 (P < 0.05). Manidipine significantly improved SG in group A from 1.60 +/- 0.64 (x 10(-2) min) to 2.19 +/- 0.38 (P < 0.05). Delapril treatment also significantly improved SG in the group B from 1.41 +/- 0.56 to 1.91 +/- 0.35 (P < 0.05). Manidipine and delapril did not affect urinary C-peptide excretion for 24 h in the hypertensive NIDDM patients. Treatment with manidipine or delapril significantly reduced systolic and diastolic blood pressures in the hypertensive NIDDM patients. There were no differences between plasma glucose, serum total triglycerides, and cholesterol or lipoprotein cholesterol fractions, heart rate and body weight after 3 months on manidipine or delapril. This study confirmed the improving effects on SI and SG by long-term treatment with manidipine or delapril in the hypertensive NIDDM patients.

Release of gastric inhibitory polypeptide (GIP) during calcium infusion and in hyperparathyroidism

Gastric inhibitory polypeptide (GIP) is a candidate hormone for an incretin which stimulates or potentiates insulin secretion. We elucidated that, in five patients with hyperparathyroidism, GIP and insulin responded remarkably to glucose ingestion, and that hypercalcaemia appeared to have a stimulatory effect on glucose-induced GIP release as well as on insulin release. In nine healthy subjects a 2% calcium solution was continuously infused intravenously and a hypercalcaemic state was maintained. This caused GIP to respond significantly more to glucose ingestion. In spite of GIP being considered an incretin in the normoglycaemic state, GIP does not markedly stimulate insulin secretion. However, in the hypercalcaemic state in healthy subjects, glucose-induced GIP and insulin secretion is significantly greater than in the normocalcaemic state. The potentiated response of insulin to glucose may be caused, in part, by GIP.