[A tooth or an implant--literature based decision making].

The common use of dental implants in the daily practice led to a profound change in the available treatment strategies. The option of replacing a diagnosed doubtful tooth with an implant has become widely accepted and often used. The prognosis systems in use today are based on the three major disciplines: endodontics, periodontics and prosthodontics. Combining these three may impair and bias the decision making process and increase the tendency to base it on subjective clinical experience and personal preference. Reading and reviewing the relevant literature gives no clear tool for use. Root canal treatment is considered a highly predictable treatment procedure and a treated tooth is affected mainly by the quality and type of the fabricated restoration and the risk of caries. Periodontal treatment followed by a suitable maintenance regimen will likely allow long term tooth survival. When comparing the success rates of natural teeth rehabilitation versus implant supported restorations, it appears that with implants an additional treatment is demanded along the years. This coincides with the fact that to date there is no consensus regarding the extent of perimplantitis and perimucositis that is to be expected around a restored implant. In addition, a peri implant tissue problem or a failure of a dental implant may prove to be more challenging than a failure of a tooth. It is important to remember that a dental implant is made to substitute a missing tooth and it is a treatment modality with known and clear indications for rehabilitation of an edentulous space. The aim of this paper is to review and discuss the various aspects of whether to maintain a compromised or a doubtful tooth or to prefer a treatment modality using dental implants. In conclusion it is advised here, to incorporate the discussed issues in the decision making process towards the most suitable treatment plan.

Evidence for a major gene affecting the transition from normoglycaemia to hyperglycaemia in Psammomys obesus.

We investigated the mode of inheritance of nutritionally induced diabetes in the desert gerbil Psammomys obesus (sand rat), following transfer from low-energy (LE) to high-energy (HE) diet which induces hyperglycaemia. Psammomys selected for high or low blood glucose level were used as two parental lines. A first backcross generation (BC(1)) was formed by crossing F(1) males with females of the diabetes-prone line. The resulting 232 BC(1) progeny were assessed for blood glucose. All progeny were weaned at 3 weeks of age (week 0), and their weekly assessment of blood glucose levels proceeded until week 9 after weaning, with all progeny maintained on HE diet. At weeks 1 to 9 post weaning, a clear bimodal distribution statistically different from unimodal distribution of blood glucose was observed, normoglycaemic and hyperglycaemic at a 1:1 ratio. This ratio is expected at the first backcross generation for traits controlled by a single dominant gene. From week 0 (prior to the transfer to HE diet) till week 8, the hyperglycaemic individuals were significantly heavier (4--17%) than the normoglycaemic ones. The bimodal blood glucose distribution in BC(1) generation, with about equal frequencies in each mode, strongly suggests that a single major gene affects the transition from normo- to hyperglycaemia. The wide range of blood glucose values among the hyperglycaemic individuals (180 to 500 mg/dl) indicates that several genes and environmental factors influence the extent of hyperglycaemia. The diabetes-resistant allele appears to be dominant; the estimate for dominance ratio is 0.97.

A novel per-oral insulin formulation: proof of concept study in non-diabetic subjects.

AIMS: The aim of our study was to examine the absorption of insulin from the gastrointestinal (GI) tract, using a novel oral formulation-adding a delivery agent SNAC (sodium N-[8-(2-hydroxybenzoyl)amino] caprylate) in combination with insulin. METHODS: Capsules containing insulin and SNAC, in various combinations, were administered orally, as a single dose, to 12 non-diabetic subjects and four control subjects (receiving SNAC or insulin only) in order to assess its biological effect and safety. Plasma glucose levels, insulin and C-peptide concentrations, as well as SNAC levels, were determined, at timed intervals up to 4 h. RESULTS: In all cases, a glucose-lowering effect was demonstrated, preceded by an increase in plasma insulin levels. The nadir of plasma glucose levels appeared after 30-50 min, following the ingestion of the mixture. The plasma insulin levels were found to parallel the blood SNAC levels. Plasma C-peptide levels were suppressed by the lowered glucose levels achieved concurrent with the increasing amount of exogenous insulin absorbed, indicating that the secretion of endogenous hormone was partially abolished. There were no biological effects regarding blood glucose levels upon administration of SNAC or insulin when given alone. No adverse effects were detected during the trial or several weeks after the trial. CONCLUSIONS: Insulin in combination with a novel delivery agent, SNAC, given orally, is absorbed through the GI tract in a biologically active form. This was demonstrated by a glucose lowering effect of the mixture as well as a suppression of an endogenous insulin secretion.

Psammomys obesus and the albino rat--two different models of nutritional insulin resistance, representing two different types of human populations.

Animal models for insulin resistance and type 2 diabetes are required for the study of the mechanism of these phenomena and for a better understanding of diabetes complications in human populations. Type 2 diabetes is a syndrome that affects 5-10% of the adult population. Hyperinsulinaemia, hypertriglyceridaemia, decreased high-density lipoprotein (HDL) cholesterol levels, obesity and hypertension, all form a cluster of risk factors that increase the risk of coronary artery disease, and are known as insulin resistance syndrome or syndrome X. The gerbil, Psammomys obesus is characterized by primary insulin resistance and is a well-defined model for dietary induced type 2 diabetes. Weanling Psammomys and Albino rats were held individually for several weeks on high energy (HE) and low energy (LE) diets in order to determine the development of metabolic changes leading to diabetes. Feeding Psammomys on HE diet resulted in hyperglycaemia (303 +/- 40 mg/dl), hyperinsulinaemia (194 +/- 31 microU/ml) and a moderate elevation in body weight, obesity and plasma triglycerides. Albino rats on HE diet demonstrated an elevation in plasma insulin (30 +/- 4 microU/ml), hypertriglyceridaemia (170 +/- 11 mg/dl), an elevation in body weight and obesity, but maintained normoglycaemia (98 +/- 6 mg/dl). Psammomys represent a model that is similar to human populations, with primary insulin resistance expressed in young age, which leads to a high percentage of adult type 2 diabetes. Examples for such populations are the Pima Indians, Australian Aborigines and many other Third World populations. The results indicate that the metabolism of Psammomys is well adapted towards life in a low energy environment, where Psammomys takes advantage of its capacity for a constant accumulation of adipose tissue that will serve for maintenance and breeding in periods of scarcity. This metabolism known as 'thrifty metabolism', is compromised at a high nutrient intake.

Circulating lipoproteins and hepatic sterol metabolism in Psammomys obesus prone to obesity, hyperglycemia and hyperinsulinemia.

The liver plays a central role in lipoprotein metabolism and cholesterol homeostasis. As the physiopathology of lipid disorders in non-insulin-dependent diabetes mellitus (NIDDM) is multifactorial and still imperfectly known, we evaluated its onset on plasma lipid transport and hepatic cholesterol metabolism in Psammomys obesus. This sand rat lapses into hyperinsulinemia and hyperglycemia when transferred from its native food to laboratory rodent diets. Marked hypertriglyceridemia and hypercholesterolemia developed in hyperinsulinemic (Group B) and hyperglycemic/ hyperinsulinemic (Group C), compared with normal P. obesus (Group A). Group B showed significantly (P<0.05) higher plasma VLDL-cholesterol (41.9%) and LDL-cholesterol (47.3%) concentrations, whereas Group C was characterized by an even more marked increase in VLDL-cholesterol (176%, P<0.001) compared with Group A. Lipoprotein composition was also altered, displaying impaired lipid and apolipoprotein moiety distribution in IDL, LDL, HDL(2) and HDL(3) lipoprotein fractions of Groups B and C. The activity of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme in cholesterol biosynthesis, was consistently lower in Group B (P<63.4%, P<0.001) and C (43.9%, P<0.005). In contrast, the direct measurement of microsomal acyl-CoA:cholesterol acyltransferase (ACAT), controlling the acylation of cholesterol, showed an increase averaging 53% in Group B (P<0.01) and 61% in Group C (P<0.005). Similarly, elevated activity (171.1%, P<0.05 and 291.4%, P<0.001, respectively) was related to cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in bile acid biosynthesis. These alterations were accompanied with abundant deposition of triglycerides and cholesterol in the liver. Changes in circulating lipids and liver parameters were related to glucose and insulin levels, indicating the implication of insulin resistance and diabetes. Therefore, our findings demonstrate various disturbances in plasma lipid profile and lipoprotein composition, as well as in liver cholesterol metabolism during the sequential development of insulin resistance and diabetes in P. obesus rats. Furthermore, the current data point to an undoubtedly important role of the liver in the pathogenesis of metabolic disorders in the progression of nutritionally-induced insulin resistance and diabetes in P. obesus. Finally, current research shows that more marked plasma and hepatic lipid perturbations occur in insulin resistance than in diabetes, which may culminate in the development of atherosclerosis.

Treatment of diabetes with vanadium salts: general overview and amelioration of nutritionally induced diabetes in the Psammomys obesus gerbil.

BACKGROUND: Numerous investigations have demonstrated the beneficial effect of vanadium salts on diabetes in streptozotocin (STZ)-diabetic rats, in rodents with genetically determined diabetes and in human subjects. The amelioration of diabetes included the abolition of hyperglycemia, preservation of insulin secretion, reduction in hepatic glucose production, enhanced glycolysis and lipogenesis and improved muscle glucose uptake through GLUT4 elevation and translocation. The molecular basis of vanadium salt action is not yet fully elucidated. Although evidence has been provided that the insulin receptor is activated, the possibility exists that cytosolic non-receptor tyrosine kinase, direct phosphorylation of IRS-1 and activation of PI3-K, leading to GLUT4 translocation, are involved. The raised phosphorylation of proteins in the insulin signaling pathway appears to be related to the inhibition of protein tyrosine phosphatase (PTPase) activity by vanadium salts. NOVEL EXPERIMENTS: The model utilized in our study was Psammomys obesus (sand rat), a desert gerbil which becomes hyperglycemic and hyperinsulinemic on an ad libitum high energy (HE) diet. In contrast to the previously investigated insulin deficient models, vanadyl sulphate was used to correct insulin resistance and hyperinsulinemia, which led to beta-cell loss. Administration of 5 mg/kg vanadyl sulfate for 5 days resulted in prolonged restoration of normoglycemia and normoinsulinemia in most animals, return of glucose tolerance to normal, and a reduction of hepatic phosphoenolpyruvate carboxykinase activity. There was no change in food consumption and in regular growth during or after the vanadyl treatment. Pretreatment with vanadyl sulfate, followed by transfer to a HE diet, significantly delayed the onset of hyperglycemia. Hyperinsulinemic-euglycemic clamp of vanadyl sulfate treated Psammomys demonstrated an improvement in glucose utilization. However, vanadyl sulfate was ineffective when administered to animals which lost their insulin secretion capacity on protracted HE diet, but substantially reduced the hyperglycemia when given together with exogenous insulin. The in vitro insulin activation of liver and muscle insulin receptors isolated from vanadyl treated Psammomys was ineffective. The in vivo vanadyl treatment restored muscle GLUT4 total protein and mRNA contents in addition to membrane GLUT4 protein, in accordance with the increased glucose utilization during the clamp study. These results indicate that short-term vanadyl sulfate treatment corrects the nutritionally induced, insulin resistant diabetes. This action requires the presence of insulin for its beneficial effect. Thus, vanadyl action in P. obesus appears to be the result of insulin potentiation rather than mimicking, with activation of the signaling pathway proteins leading to GLUT4 translocation, probably distal to the insulin receptor.

Effects of variations in food intake on renal sodium pump activity and its gene expression in Psammomys kidney.

Psammomys obesus lives in an arid environment and feeds on saltbush. When animals are fed a laboratory diet, urine osmolarity drops. To explore the mechanism(s) of water conservation, we measured renal function, kidney solute content, Na-K-ATPase activity, and mRNA in several groups: group I (saltbush diet, 18 g/day, 4.2 g protein); group II (laboratory diet, 10 g/day, 1.8 g protein); and group III, the same as group I, and group IV, the same as group II, both plus a 1-day fast. Urine osmolarity was 2,223 +/- 160, 941 +/- 144, 1,122 +/- 169 and 648 +/- 70.9 mosM in groups I, II, III, and IV, respectively. Tissue osmolarities in cortex, outer medulla, and inner medulla, respectively, were 349 +/- 14, 644 +/- 63, and 1,152 +/- 34 microosM/mg tissue in group I; 317 +/- 24, 493 +/- 17, and 766 +/- 60 microosM/mg tissue in group II; 335 +/- 6, 582 +/- 15, 707 +/- 35 microosM/mg tissue in group III; and 314 +/- 18, 490 +/- 22, and 597 +/- 29 microosM/mg tissue in group IV. There were no differences in Na-K-ATPase activity and mRNA in cortex and in medulla between groups I and II, whereas in group III Na-K-ATPase activity and mRNA increased in cortex and outer medulla. These results suggest a key role for urea in corticomedullary osmotic gradient of Psammomys. The absence of differences in Na-K-ATPase activity and mRNA between groups I and II despite differences in tissue sodium concentrations is consistent with Na-K-ATPase-independent Na absorption. Increased Na-K-ATPase activity and mRNA in fasting suggest transition to Na-K-ATPase- dependent Na transport.

Renal Na-K-ATPase hyperactivity in diabetic Psammomys obesus is related to glomerular hyperfiltration but is insulin-independent.

Psammomys obesus, a desert rodent, develops diabetes when displaced from its natural environment and fed a high energy diet in the laboratory. This study was designed to examine variations in renal function in relation to the diabetic state with emphasis on changes in Na-K-ATPase activity. The following groups of Psammomys were studied: (1) Animals fed a saltbush diet; a low energy/high salt diet (natural). (2) Animals fed a low energy/low salt diet (laboratory). Both 1 and 2 were normoglycemic and normoinsulinemic and thus served as control. (3) Animals fed a high energy diet (group C) who were hyperglycemic and hyperinsulinemic; this group was divided into two subgroups: C1 presented with glomerular hyperfiltration rate and C2 with glomerular hypofiltration rate. (4) Animals fed a high energy diet presenting with hyperglycemia-hypoinsulinemia (group D). (5) Group D+I, similar to group D but treated with external insulin (2 U/24 h). Groups D and C1, whose glomerular filtration rose above normal by 30% and 70% respectively, exhibited metabolic similarity to Type I and Type II diabetes. In these groups, Na-K-ATPase activity in the cortex increased by 80-100% and in the medulla by 180% (P<0.001 vs control). In group C2 with reduced glomerular filtration rate (GFR), Na-K-ATPase activity did not differ from control. In group D+I, with normalized glomerular filtration rate, Na-K-ATPase activity was similar to control. There was a linear and significant correlation between GFR and Na-K-ATPase activity both in the cortex and in the medulla. These experiments present a well defined animal model of diabetes mellitus. Variations in glucose and in insulin did not correlate with Na-K-ATPase activity. These results clearly demonstrated that Na-K-ATPase activity in the diabetic Psammomys was determined by glomerular filtration but was independent of plasma glucose or insulin levels.

A sustained, non-insulin related, hypoglycaemic effect of electroacupuncture in diabetic Psammomys obesus.

AIM/HYPOTHESIS: Electroacupuncture has been shown to induce a short-term hypoglycaemic effect in streptozotocin diabetic rats. We designed an experiment to investigate the effect of electroacupuncture in Psammomys obesus, a model of insulin resistance and non-insulin-dependent diabetes mellitus. METHODS: We divided 29 diabetic Psammomys randomly into three groups: abdominal electroacupuncture (real, n = 11), back electroacupuncture (placebo, n = 9) and control (anaesthesia, n = 9). Electroacupuncture was carried out on days 1, 3 and 5 of the experiment. During the first week of the experiment, blood glucose was tested three times on treatment days and once on the following days. Over the next 2 weeks, blood glucose was tested every other day. Animals were weighed at the same time of blood sampling. After 3 weeks, at the end of the experiment, blood was drawn for measurement of insulin, fructosamine, cholesterol and triglycerides. RESULTS: At day 5 (end of intervention), blood glucose (as per cent of primary concentrations, means +/- SE) was 57 +/- 10, 93 +/- 13 and 89 +/- 11 for the real, placebo and control groups respectively (p = 0.02). At day 8, blood glucose 68 +/- 14, 86 +/- 16 and 97 +/- 9 for the real, placebo and control groups respectively (p = 0.04). At day 22, blood glucose was 79 +/- 11, 85 +/- 15 and 131 +/- 2 for the real, placebo and control groups (p = 0.04). Comparison of the decline in blood glucose, throughout the 3 weeks, between the real and placebo groups by ANOVA was highly significant (p < 0.0001), the difference between the placebo and control groups at the same time was not significant (p > 0.05). Animal weight gain, serum insulin, fructosamine, cholesterol and triglycerides were not significantly different between real and placebo groups. CONCLUSION/INTERPRETATION: Electroacupuncture at special abdominal acupoints induces a sustained hypoglycaemic effect in diabetic Psammomys compared with electroacupuncture at non-specific points, without weight loss. No hypoinsulinaemic effect was shown in the real and placebo groups.

Plasma total homocysteine levels in subjects with hyperinsulinemia.

OBJECTIVES: Hyperhomocysteinemia as well as insulin resistance are considered to be risk factors for the development of coronary artery disease. This study was aimed at determining whether any relationship between plasma insulin and glucose levels and total plasma homocysteine (tHcy) concentrations exists in a population based survey performed 10 years apart. DESIGN AND SETTING: A cross-sectional study was undertaken during the years 1986-87 to examine risk factors for diabetes and for coronary artery disease (CAD) in the Jewish population of Jerusalem. Ten years later two groups of individuals were invited for re-examination. SUBJECTS: Two groups of individuals were examined: the first one consisted of nondiabetic subjects (n = 86), who had hyperinsulinemia 10 years previously (at the first visit), the second group consisted of normoinsulinemic nondiabetic individuals (n = 265) who had initially normal glucose and insulin levels. MAIN OUTCOME MEASURES: Metabolic, biochemical and anthropomorphic features were determined. Fasting and post load glucose, as well as insulin concentrations on fasting and 2 h post glucose load were measured at the first and second visits. Plasma tHcy and folic acid were determined only at the second visit. RESULTS: The results demonstrated a significant negative correlation between plasma tHcy levels and insulin levels at the second visit. No difference was found in folic acid levels between these two groups. CONCLUSIONS: In general, hyperinsulinemia and hyperhomocysteinemia are both related to an increased incidence of CAD. In our population most of the subjects examined had tHcy levels within the normal range and only a few demonstrated very high levels. However, negative association between insulin levels and tHcy concentrations was found. Possible explanations for this finding are discussed.

Low density lipoprotein particle size and risk factors of insulin resistance syndrome.

The present study aimed to examine the association between low density lipoprotein (LDL) particle size and glucose and insulin variables and with other risk factors that have been related to insulin resistance syndrome. LDL particle size was determined in two groups of subjects who participated in the first examination of the Jerusalem Diabetes Study and who were invited to be re-examined after 8-10 years. The first group were non-diabetic subjects who were found to have at the first examination high insulin levels (above the sex and age specific 90th percentile of the 2 h post-glucose load insulin distribution). The second group was a random sample of individuals who had normal insulin and glucose levels at baseline. Sex-, Age- and body mass index (BMI) mean adjusted LDL-cholesterol (C), triglyceride (TG) and high density lipoprotein cholesterol (HDL-C) levels were significantly different among the LDL subclass groups. Fasting glucose levels and hemoglobin A(1c) did not differ statistically by LDL subclasses. Fasting and 2-h post load insulin levels were significantly higher in persons with LDL subclasses III and IV (small LDL), intermediate in those with LDL subclass II, and lowest in those with LDL subclass I (large LDL). Insulin resistance had an effect on the association between lipids, lipoproteins and LDL particle size. Multivariate analyses indicated that LDL-C, HDL-C and TG were independently associated with LDL particle size variability. The addition of 'insulin resistance' or insulin and glucose levels had no independent effects on LDL particle size. In conclusion, an association of LDL particle size with the cluster of risk factors that characterize the insulin resistance syndrome has been demonstrated. The association of 'insulin resistance' and LDL particle diameter, however, is not mediated directly through the level of insulinemia but via alterations in lipid metabolism.

Intestinal absorption of low molecular weight heparin in animals and human subjects.

INTRODUCTION: We had previously shown that the use of bile salts, which act as surfactants, facilitates the intestinal absorption of large molecules such as those of heparin and insulin. However, the bioavailability of unfractionated heparin (UFH) administered through the large intestine was low. The aim of the present study was to evaluate the absorption of low molecular weight heparin (LMWH) combined with bile salts through the gut mucosa in animals and human subjects. MATERIALS AND METHODS: LMWH (Fragmin, Kabi-Pharmacia, Stockholm) or UFH with or without sodium cholate (Sch) was administrated rectally in rats and healthy volunteers via a microenema. Absorption was estimated by the activated partial thromboplastin time (aPTT), the plasma anti-factor Xa activity and the plasma lipoprotein lipase (LPL) activation. RESULTS: In groups of 6 rats, LMWH at doses of 100--1,000 U with sodium cholate (10--20 mg/ml) was readily absorbed through the gut mucosa, as indicated by both, anti-factor Xa levels of up to 1 U/ml and a dose-dependent activation of LPL. The absorption was significantly superior to that of UFH with Sch or LMWH given without Sch (p < 0.001). The plasma anti-factor Xa levels in the 6 healthy volunteers who received a microenema containing 25,000 U of LMWH with 20 mg/ml of Sch were 0.38 U/ml at 15 min and 0.1 U/ml at 240 min. LPL activation and aPTT prolongation were also observed in these subjects. The plasma LMWH levels after rectal application were in the same range as those obtained after subcutaneous administration, however the elimination time (t 1/2) was shorter. There were no adverse reactions. CONCLUSIONS: Intestinal absorption of LMWH facilitated by Sch is both feasible and safe. A slow release formulation will be needed to prolong the plasma half-life.

Ageing and the mismatch repair system.

Age-related accumulation of mutations has been extensively documented, and it has been proposed as one of the prominent causes of malignancies in old age. The present review is focused on the particular case of DNA mismatch repair system (MMR), that has drawn increased attention for its possible relevance to malignancy. We also report on our own observations on an age-associated genomic instability that develops with age in the MMR system. Our study was performed on DNA samples that were prepared from peripheral blood cells, obtained at a 10-year interval from young and old human subjects. The two DNA samples from each individual were examined comparatively. The older individuals showed a significantly higher rate of microsatellite instability (MSI) in several loci examined, whereas no difference was found between the paired samples of any of the young subjects. We suggest that this increase in MSI with age may indicate an overall genomic instability in the elderly.

Changing pattern of prevalence of insulin resistance in Psammomys obesus, a model of nutritionally induced type 2 diabetes.

Psammomys obesus (a desert gerbil, nicknamed the "sand rat") with innate insulin resistance was transferred to a high-energy (HE) diet at a young (8 to 20 weeks) and older (38 to 45 weeks) age. The young Psammomys progressed to in vivo insulin resistance, followed by pronounced hyperglycemia and hyperinsulinemia, as described previously. Analysis of the time dependency of these changes in response to the HE diet showed that the increase in serum glucose preceded the increase in insulin and plateaued earlier, reverting to normal together with insulin in the older Psammomys. Implants releasing insulin 2 IU/24 h did not induce appreciable hypoglycemia, a decrease in free fatty acids (FFAs), or a suppression of hepatic phosphoenolpyruvate carboxykinase (PEPCK) activity in young animals after 5 hours, despite a markedly increased circulating insulin. However, in the older Psammomys, the exogenous hyperinsulinemia produced a significant decline in serum glucose and FFA and a suppression of hepatic PEPCK activity. A euglycemic-hyperinsulinemic clamp confirmed that hepatic glucose production (HGP) was lower in older Psammomys versus the young and was almost completely abolished by insulin (from 5.6 +/- 0.6 to 0.2 +/- 0.1 mg x min(-1) x kg(-1) v 10.9 +/- 0.8 to 3.9 +/- 0.5 mg x min(-1) x kg(-1)). This indicates that HGP, rather than glucose underutilization, was the main contributor to the hyperglycemia and that the hepatic insulin resistance in Psammomys is attenuated with age. In relation to the human condition, these findings point out that while the type 2 diabetes prevalence in Western populations generally increases with age, the excessive nutritional intake in high-risk populations produces a pattern of diabetes prevalence that tapers off with age. As such, the nutritionally induced diabetes in Psammomys represents a similar model for a differing pattern of the age-related prevalence of diabetes.

A common mutation A1298C in human methylenetetrahydrofolate reductase gene: association with plasma total homocysteine and folate concentrations.

Methylenetetrahydrofolate reductase (MTHFR) is one of the main regulatory enzymes of homocysteine metabolism. Previous studies revealed that a common mutation in MTHFR gene C677T is related to hyperhomocysteinemia and occlusive vascular pathology. In the current study, we determined the prevalence of a newly described mutation in the human MTHFR gene A1298C, and the already known C677T mutation, and related them to plasma total homocysteine and folate concentrations. We studied 377 Jewish subjects, including 190 men and 186 women aged 56.8 +/- 13 y (range 32-95 y). The frequency of the homozygotes for the A1298C and the C677T MTHFR mutations was common in the Jewish Israeli population (0.34 and 0.37, respectively). Subjects homozygous (TT) for the C677T mutation had significantly greater plasma total homocysteine concentrations (P < 0.01) than subjects without the mutation (CC). Homozygotes (CC) for the A1298C mutation did not have elevated plasma total homocysteine concentrations. Our study indicated that subjects with the 677CC/1298CC genotype had significantly lower concentrations (P < 0. 05) than those with a 677CC/1298AA genotype. Neither mutation (the A1298C and the C677T) was associated with established cardiovascular risk factors such as hypertension, elevated total cholesterol or body mass index.

Irreversibility of nutritionally induced NIDDM in Psammomys obesus is related to beta-cell apoptosis.

Psammomys lapses into fully fledged diabetes when maintained on a high-energy diet. Progression to diabetes has been classified into stage A of normoglycemia and normoinsulinemia (<120 mg/ml and 100 mU/L, respectively); stage B of hyperinsulinemia (100-300 mU/L) with marked insulin resistance in the face of normoglycemia; stage C of pronounced hyperinsulinemia with hyperglycemia < or =500 mg/ml; stage D at 6-10 weeks after stage C, featuring further hyperglycemia and loss of insulin. Insulin resistance expressed in Psammomys at stages B and C was demonstrated by nonsuppression of the hepatic gluconeogenesis enzyme phosphoenolpyruvate carboxykinase by the endogenous hyperinsulinemia and by the reduced capacity of insulin to activate muscle and liver tyrosine kinase of the insulin receptor. Diabetes at stage C, but not at stage D, was fully reversed to stage A by restricting the food ration of animals by half (from 14 to 7 g/day) for 10-14 days. We examined islet beta cells of Psammomys in the four stages of progression to diabetes by staining for insulin as well as for apoptosis by the terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) and visualizing the biotin-labeled cleavage sites. Psammomys in stage A had insulin-laden beta cells. In stage B, a hypertrophy and partial insulin depletion of beta cells was evident with negative TUNEL staining. In stage C, beta cells were markedly depleted of insulin, and their number within the islets decreased, but the TUNEL staining was virtually negative. In stage D, beta cells were markedly diminished within the islets, almost void of insulin, showing distinct TUNEL staining of beta cells. These results indicate that prolonged exposure of islets to in vivo hyperglycemia with beta-cell overtaxation induces nuclear disintegration with irreversible damage to the insulin-secretion apparatus. This precludes the return to normalcy by restricting the food intake of Psammomys. The appearance of cells with TUNEL-positive staining may serve as a marker of impending irreversibility of nutritionally induced diabetes.

Dolichol-mediated enhanced protein N-glycosylation in experimental diabetes--a possible additional deleterious effect of hyperglycemia.

In liver cells from diabetic rats, an increased incorporation of labeled glucosamine into cellular and secretory proteins was found, when related to the incorporation of labeled leucine. This increased N-glycosylation was present in the face of decreased synthesis of hepatic cellular and secretory proteins evident from reduced leucine incorporation and diminished glycosyltransferase activity. To elucidate the mechanisms involved we incubated isolated hepatocytes with two N-glycosylation inhibitors: tunicamycin and 2-deoxyglucose. Tunicamycin exerted a marked inhibitory effect on the incorporation rate of labeled glucosamine into proteins in liver cells from diabetic rats, while 2-deoxyglucose had a negligible effect on this process in these cells. These diverse effects might be explained by the fact that tunicamycin acts through strong association with the enzyme catalyzing the first step in glycoprotein synthesis, namely, the transfer of UDP-GlcNAc to dolichol-P (indicating noncompetitive inhibition). This enzyme is reduced in liver cells from diabetic animals. On the other hand, 2-deoxyglucose exerts its effect by being attached to dolichol-P, preventing further elongation of oligosaccharide chain on the protein backbone. This latter effect might be eliminated by excess dolichol-P (indicating competitive inhibition). The dolichol content in liver extract from diabetic rats was about 2.5-fold higher compared with nondiabetic rats (51.6 micrograms/g versus 20.6 micrograms/g wet liver weight). These two lines of evidence confirm the notion that the enhanced enzymatic glycosylation in liver from diabetic animals is maintained by an increased hepatic dolichol concentration, which is most probably related to the hyperglycemia. Thus, the dolichol-N-glycosylation pathway may represent another detrimental aspect of hyperglycemia and may operate by dolichol mass action rather than through glycosylating enzyme activity.

Insulin resistance in the NIDDM model Psammomys obesus in the normoglycaemic, normoinsulinaemic state.

The desert gerbil Psammomys obesus ("sand rat"), a model of nutritionally induced insulin resistance and non-insulin-dependent diabetes mellitus, was treated after weaning with exogenous insulin implants in the normoglycaemic, normoinsulinaemic state. Albino rats matched for weight and age served as high energy diet adjusted reference animals. Insulin administration, elevating the serum insulin to 6000 pmol/l resulted in only a mild reduction in blood glucose levels in Psammomys, but caused a severe, often fatal hypoglycaemia in the albino rats. The hepatic response to insulin-induced hypoglycaemia in rats involved a significant loss in glycogen and suppression of phosphoenolpyruvate carboxykinase (PEPCK) activity. In Psammomys under similar hyperinsulinaemia no appreciable changes in liver glycogen and PEPCK activity were evident, indicating that blood glucose was replenished by continuing gluconeogenesis. Euglycaemic, hyperinsulinaemic clamp caused a complete shut-down of hepatic glucose production in albino rats. However, in both diabetes-prone and diabetes-resistant Psammomys lines, mean hepatic glucose production was reduced by only 62 to 53% respectively, despite longer lasting and higher levels of hyperinsulinaemia. These results indicate that Psammomys is characterized by muscle and liver insulin resistance prior to diet-induced hyperglycaemia and hyperinsulinaemia. This is assumed to be a species feature of Psammomys, exemplifying a metabolic adjustment to survival in conditions of food scarcity of both animal and human populations. It may reflect a propensity to insulin resistance and hyperglycaemia in population groups exposed to affluent nutrition.