A high protein low fat meal does not influence glucose and insulin responses in obese individuals with or without type 2 diabetes.

BACKGROUND: When substituted for carbohydrate in a meal, dietary protein enhances glycaemic control in subjects with type 2 diabetes (DM2). It is unknown whether the effect is a result of increased protein or reduced carbohydrate. The present study aimed to compare the effects of two meals differing in protein to fat ratios on post-prandial glucose and insulin responses. METHODS: This was a crossover, blind study in which obese subjects with (n = 23) and without (n = 26) DM2 consumed two meals in random order with equal amounts of energy (3.1 MJ, 741 kcal), fibre and carbohydrates and a 1-week washout period. Meals were a high protein, low fat (30% protein, 51% carbohydrates, 19% fat) meal and a low protein, high fat (15% protein, 51% carbohydrates, 34% fat) meal. Subjects were matched for age and body mass index. Plasma glucose and insulin were measured at fasting, 30, 60, 90, 120 min post-prandially. Insulin resistance and insulin sensitivity were assessed. RESULTS: There was no significant meal effect on glucose and insulin responses within groups. Glucose response was higher in diabetic (120 min 11 +/- 0.7 mmol L(-1)) compared to nondiabetic (120 min 5 +/- 0.2; P < 0.001) subjects. Diabetic subjects had significantly higher insulin resistance (P < 0.001) and lower insulin sensitivity (P < 0.001) than nondiabetics. Although peak insulin levels, 60 min post-prandially, did not differ between groups (81 +/- 9 pmol L(-1) for diabetic versus 79 +/- 7 pmol L(-1) for nondiabetic subjects), they were achieved much later, 90 min post-prandially, in diabetic, (99 +/- 8 pmol L(-1)) compared to nondiabetic (63 +/- 7 pmol L(-1), P = 0.002) subjects. CONCLUSIONS: Manipulating protein to fat ratio in meals does not affect post-prandial plasma blood glucose or insulin responses in obese people with and without DM2.

Role of vitamin A in mitochondrial gene expression.

Diabetes-prone BHE/Cdb and Sprague-Dawley (SD) rats were studied with respect to mitochondrial (mt) function and mt gene expression. The BHE/Cdb rats carry mutations in the mt ATPase 6 gene that phenotype as decreased OXPHOS efficiency with subsequent development of impaired glucose tolerance. The base substitutions result in amino acid substitutions in the proton channel and this, in turn, affects the efficiency of energy capture in the ATP molecule. Feeding studies showed that BHE/Cdb rats required 10 times more vitamin E and three times more vitamin A in their diets than do normal SD rats. Vitamin A supplementation 'normalized' mt OXPHOS as well as increased the amount of ATPase subunit a protein in the mt compartment. Western blot analysis of retinoic acid receptors in the mitochondrial and nuclear compartments showed that these proteins were present in the mt compartment. The effect of the vitamin A supplementation plus the observation of retinoic acid receptors suggest that vitamin A functions to enhance the transcription of the ATPase 6 gene. Work with primary cultures of hepatocytes showed that not only does retinoic acid increase mitochondrial ATPase 6 gene expression but so too does the steroid hormone intermediate, dehydroepiandrosterone (DHEA). Triiodothyronine also plays a role in this process but not as an independent factor. Rather, this hormone potentiates the effects of retinoic acid and DHEA on ATPase gene expression. These results suggest that mt gene expression requires more than just the mt transcription factor A. More than likely the process requires a number of factors in much the same way as does nuclear gene expression.

Mitochondrial gene expression in diabetes mellitus: effect of nutrition.

Diabetes mellitus is a collection of genetic diseases that share a common phenotype: glucose intolerance. The genetic origins of this disease are being widely investigated. An estimated 0.19% of the population with diabetes has the disorder owing to one or more mutations in the mitochondrial genome. Diet can affect the expression of the genome as well as the function of its gene products. The antioxidant nutrients serve to protect this very vulnerable genome from oxidative damage. These nutrients may affect mitochondrial DNA transcription and nutrients that affect membrane fluidity affect the function of the gene products.

Mitochondrial DNA in aging and degenerative disease.

The mitochondrial DNA encodes only a few gene products compared to the nuclear DNA. These products, however, play a decisive role in determining cell function. Should this DNA mutate spontaneously or be damaged by free radicals the functionality of the gene products will be compromised. A number of mitochondrial genetic diseases have been identified. Some of these are quite serious and involve the central nervous system as well as muscle, heart, liver and kidney. Aging has been characterized by a gradual increase in base deletions in this DNA. This increase in deletion mutation has been suggested to be the cumulative result of exposure to free radicals.

Diabetes and nutrition: the mitochondrial part.

Diabetes mellitus is the most common genetic disease in the Western world today. It is the phenotype for >150 genotypes. Each of these genotypes is characterized by impaired glucose tolerance and impaired control of intermediary metabolism. There are many strains of mice and rats that can be used to study diabetes in its various forms. One of these is the BHE/Cdb rat, which mimics the human phenotype with a mutation in the mitochondrial (mt) DNA. The result of such mutation is a loss in metabolic control with respect to the role of the mitochondria in this control. This review addresses those aspects of control that are exerted by mt oxidative phosphorylation (OXPHOS). Diet can have both genomic and nongenomic effects on OXPHOS. The type of dietary fat influences the fluidity of the mt membranes and hence, mt function. The dietary fat effect depends on the genetic background of the consumer. Diabetes-prone BHE/Cdb rats with base substitutions in the mt ATPase 6 gene are more likely to be influenced by the diet effect on mt membrane fluidity than are normal rats. Vitamin A also affects mt function through an effect on mt gene expression. BHE/Cdb rats have a greater need for vitamin A than normal rats and supplemental vitamin A appears to influence OXPHOS.

Attenuation of circadian rhythms of food intake and respiration in aging diabetes-prone BHE/Cdb rats.

The hypothesis that BHE/Cdb rats with mutations in their mitochondrial genome might accommodate this mutation by changing their food intake patterns was tested. Four experiments were conducted. Experiments 1 and 2 examined food intake patterns of BHE/Cdb rats fed a stock diet or BHE/Cdb and Sprague-Dawley rats fed a high-fat diet from weaning. Experiment 3 examined the daily rhythms of respiration and heat production in these rats at 200 days of age. Experiment 4 examined the effects of diet composition on these measurements at 50-day intervals. The Sprague-Dawley rats, regardless of diet, had the typical day-night rhythms of feeding and respiration. In contrast, the BHE/Cdb rats fed the high-fat diet showed normal rhythms initially, but with age, these rhythms were attenuated. The changes in rhythms preceded the development of glucose intolerance.

Oligomycin sensitivity of mitochondrial F(1)F(0)-ATPase in diabetes-prone BHE/Cdb rats.

BHE/Cdb and Sprague-Dawley rats differ in their mitochondrial DNA sequence for the ATPase 6 ("subunit a") gene. Base substitutions in this sequence result in the substitution of asparagine for aspartate at position 101 and the substitution of serine for leucine at position 129. Differences in sensitivity to oligomycin were observed. When the isolated F(1)F(0)-ATPase complex was studied and ATPase activity was assessed, that which was isolated from the BHE/Cdb rats was less sensitive to oligomycin inhibition than that which was isolated from the Sprague-Dawley rats. In contrast, when oxygen consumption was measured [oxygen phosphorylation (OXPHOS)] and a dose-response curve was generated with isolated mitochondria from these two strains, there was a shift to the left for the BHE/Cdb rat mitochondria. These mitochondria were more sensitive to oligomycin inhibition of OXPHOS than were mitochondria isolated from Sprague-Dawley rats. The OXPHOS results are consistent with those from human fibroblasts having either a normal or mutated ATPase 6 gene.

Inheritance of a mitochondrial DNA defect and impaired glucose tolerance in BHE/Cdb rats.

As they age, BHE/Cdb rats develop impaired glucose tolerance. We hypothesized that this intolerance is associated with a previously reported base substitution in the mitochondrial genome. A new screening test was devised to identify animals with the mutation. These animals were bred to animals without the mutation. The progeny were then tested for the presence of the mutation and their glucose tolerance at 100 and 300 days of age. Phenotype and genotype were found to be closely linked and we conclude that the mutation in the mitochondrial ATPase 6 gene explains the age related impaired glucose tolerance in BHE/Cdb rats.

Further studies of diabetes-prone BHE/Cdb rats: increased sensitivity to calcium ion suppression of oxidative phosphorylation.

The responsiveness of hepatic mitochondria isolated from hyperthyroid and control Sprague-Dawley (SD) and diabetes-prone BHE/Cdb rats was studied. Hyperthyroidism was induced through the addition of thyroxine (T(4)) to the diet (2 mg/kg of diet). Oxidative phosphorylation (OXPHOS) with the addition of adenosine diphosphate (ADP) or an 8:1 mixture of adenosine monophosphate (AMP):ADP was studied. Dose response curves of state 3 and state 4 respiration, respiratory control (RC) ratio, and ADP:O ratio to calcium levels (0-7.5 microm) were generated. Mitochondria from BHE/Cdb rats were more sensitive to the addition of calcium than mitochondria from SD rats, as judged by losses in OXPHOS. T(4) treatment potentiated this strain difference and we conclude that the diabetes phenotype in the BHE/Cdb rat is probably related not only to the previously described mutation in the F(O)ATPase but also to a defect in the efflux of the calcium ion that, in turn, affected the regulation of OXPHOS.

Noninsulin-dependent diabetes mellitus as a mitochondrial genomic disease.

The genetics of diabetes mellitus is very complex. Although the phenotypes are relatively simple vis-a-vis an abnormal glucose-insulin relationship, a number of genotypes share this phenotype. This review focuses on mutations in the mitochondrial genome that phenotype as diabetes mellitus. Studies in the human and the rat are described.

Whole-egg diet delays the age-related impaired glucose tolerance of BHE/Cdb rats.

The effects of dietary egg on the age-related progression of impaired glucose tolerance and glomerulonephropathy in diabetes-prone BHE/Cdb rats were studied. This rat strain mimics the human with NIDDM. The development of impaired glucose tolerance was delayed in rats fed the whole-egg diet, however, feeding this diet resulted in elevated hepatic weight but had no effect on the age-related changes in renal lesions or renal function. We conclude that in this animal model for NIDDM, the development of glomerulonephropathy is independent of the development of impaired glucose tolerance and that diet can affect the time course for impaired glucose tolerance without affecting renal disease development.

Nutrient-gene interactions determine mitochondrial function: effect of dietary fat.

The effect on mitochondrial respiration of feeding hydrogenated coconut oil, corn oil, or menhaden oil (MO) to diabetes-prone BHE/cdb rats and normal Sprague Dawley (SD) rats was studied. Both fat source and strain affected the temperature dependence of succinate-supported respiration. The transition temperature was greater in BHE/cdb rats than in the SD rats. The efficiency of ATP synthesis as reflected by the ADP:O ratio was decreased in the BHE/cdb rats compared to SD rats, with the exception of the comparison made at 37 degrees C with the MO-fed rats; at this temperature, the ADP:O ratios were similar. The diet and strain differences suggest a dietary lipid-gene interaction with respect to the mobility of subunit 6 of the F1F0ATPase. This subunit has two errors in its gene: one that affects the proton channel and another that likely affects its mobility within the inner mitochondrial membrane.

Low dietary protein impairs blood coagulation in BHE/cdb rats.

The influence of dietary protein on blood coagulation tests was evaluated in BHE/cdb rats. Three experiments were conducted in order to compare effects of diets with low (8 g/100 g diet) or high (38 g/100 g diet) protein, to establish values for coagulation tests at intermediate (12-30 g/100 g diet) concentrations of dietary protein, and to compare feeding identical quantities of diets with 8 g protein/100 g diet vs. 18 g protein/100 g diet. After 4 wk of feeding the semipurified diets, bleeding time exceeded 15 min in the groups fed low protein diets, compared to a range of 3-6 min for the groups fed high protein diets. Several in vitro tests of coagulation were abnormal in the rats fed low protein diets. For example, prothrombin time averaged 27 +/- 8 s in rats fed 8 g protein/100 g diet plus beef tallow, but 17 +/- 1 s in rats fed 38 g protein/100 g diet plus tallow. The coagulation deficit in rats fed low protein was not affected by fat source (tallow vs. menhaden oil), but fibrinogen was elevated in rats fed diets with menhaden oil. Conversely, no differences in coagulation tests were observed among rats fed 12-30 g protein/100 g diet. Bleeding times ranged from 7 to 9 min, and prothrombin time was 17-18 s. Significant differences in plasma fibrinogen concentration and prothrombin time were observed in rats fed 8 vs. 18 g protein/100 g diet at a fixed rate of 6 g/100 g body weight. Platelet and blood cell numbers were unaffected by dietary protein. The evidence for multiple deficits in the coagulation system suggests that hepatic function in BHE/cdb rats may become impaired when the rats are fed low protein diets of the composition used here.

Differential hepatic and renal cholesterol levels in diabetes-prone BHE/cdb rats fed menhaden oil or beef tallow.

A series of experiments were conducted to determine whether the feeding of beef tallow compared with menhaden oil would affect renal cortex membrane composition, Na,K-ATPase activity, renal cholesterol uptake, and plasma lipoprotein cholesterol profile. BHE/cdb rats were used because they carry a genetic trait for non-insulin-dependent diabetes mellitus and are prone to develop diabetic nephropathy. Beef tallow feeding resulted in an increase in HDL cholesterol and an increase in Na,K-ATPase activity. The different fats also affected the arachidonic acid content of the membrane but not the membrane cholesterol content. These diet effects may explain why the development of renal disease in beef tallow-fed rats is delayed when compared with rats fed an equivalent amount of menhaden oil.

A point mutation in the mitochondrial DNA of diabetes-prone BHE/cdb rats.

Mitochondrial DNA was extracted from hepatic tissue of 50- and 300-day-old male BHE/cdb and Sprague-Dawley rats. The complete gene for the F0ATPase subunits 6 and 8 was sequenced. Four nucleotide substitutions were found: three of the substitutions were silent; the other substitution at position 523 was not. Its codon dictates the substitution of asparagine for aspartic acid in a critical location (in the polar pocket) of the F0ATPase. It is possible that this point mutation may explain previously reported decreases in ATP synthesis efficiency in BHE/cdb rats compared to Sprague-Dawley rats.

Menhaden oil feeding increases potential for renal free radical production in BHE/cdb rats.

The effects of feeding 9% beef tallow (BT) or menhaden oil (MO) in a 10% fat-60% sucrose-20% protein diet on renal cortex fatty acid profile, renal lipid peroxide formation potential, and the blood pressure response to a norepinephrine challenge was studied. Male weanling BHE/cdb prediabetic rats were studied after 8 weeks of diet treatment. Half the rats were subjected to a norepinephrine challenge, and their mean arterial blood pressure was determined. Plasma renin and angiotensin II levels were determined in the presence or absence of the challenge. The source of dietary fat had no effect on these measurements. MO fed rats had a greater potential to form lipid free radicals in the kidney than BT fed rats despite the fact that the renal tissue from both groups had an equivalent number of unsaturations on a mole % basis. From these results we conclude that the accelerated renal disease in menhaden oil fed rats is not due to a diet fat effect on blood pressure regulation but might be due to a diet fat effect on free radical production. These free radicals can be cytotoxic and if produced in large amounts could result in a loss of glomerular cells. Whether this occurs and can be reversed by a change in diet was not determined.

Diet, autoimmunity, and insulin-dependent diabetes mellitus: a controversy.

Insulin-dependent diabetes mellitus (IDDM) is a serious disorder comprising approximately 10% of the total diabetic population. The majority of the genetic mutations that result in the phenotypic expression of the IDDM genotype are in the immune system. In some, the disease arises as a consequence of a viral infection. While some viruses target the islet beta cell and destroy it, other viruses induce changes in the antigen recognition system such that the affected individual appears to have autoimmune disease. Autoimmune-IDDM results from one or more mutations in the immune system that result in a failure to distinguish self antigens from foreign antigens. As a result, the beta cells of the endocrine pancreas are destroyed. This review addresses the issue of whether dietary factors, in particular, milk protein, can initiate the autoimmune process. Based on the population studies available in the literature, the conclusion is reached that, while antibodies to milk proteins can be found in the patient with autoimmune diabetes mellitus, these antibodies were probably elicited by a closely related protein (antigen mimicry). Because one of the features of autoimmune disease is a loss of antibody specificity, cross-reactivity occurs and appears to identify milk protein(s) as the antigen.

In situ glucose uptake and glucokinase activity of pancreatic islets in diabetic and obese rodents.

The present study evaluated the involvement of glucose transport and phosphorylation in glucose-stimulated insulin release from pancreatic islets. Using quantitative histochemical techniques, we investigated basal islet glucose content, islet glucose uptake in situ during acute extreme experimental hyperglycemia, and islet glucokinase activity in several animal models of diabetes and obesity. The basal islet glucose content in anaesthetized diabetic or obese rodents was either the same or higher than that in their relevant controls. The rate of glucose uptake of islet tissue in these animals after an i.v. glucose injection was different. The db+/db+ mouse and the obese Zucker rat exhibited significantly reduced islet glucose uptake rates. RIP-cHras transgenic mice, BHE/cdb rats and partially pancreatectomized rats showed normal islet glucose uptake rates. The activity of islet glucokinase was increased to a different degree related to the blood glucose level. All five animal models of diabetes or obesity exhibited either a delay or a reduction of insulin release in response to supra maximal glucose stimulation. Our results indicate that the impairment of glucose-induced insulin release in diabetes is not consistently associated with a reduction of islet glucose uptake nor a change of glucokinase activity.