Polymorphism in the Calpain 10 gene influences glucose metabolism in human fat cells

Arsenic impairs GLUT1 trafficking through the inhibition of the calpain system in lymphocytes

Exposure to arsenic is associated with increased risk of developing insulin resistance and type 2 diabetes. The proteases calpain-1 (CAPN1), calpain-2 (CAPN2) and calpain-10 (CAPN10) and their endogenous inhibitor calpastatin (CAST) regulate glucose uptake in skeletal muscle and adipocytes. We investigated whether arsenic disrupts GLUT1 trafficking and function through calpain inhibition, using lymphocytes as a cell model. Lymphocytes from healthy subjects were treated with 0.1 or 1 μM of sodium arsenite for 72 h and challenged with 3.9 or 11.1 mM of glucose. Our results showed that arsenite inhibited GLUT1 trafficking, glucose uptake, and calpain activity in the presence of 11.1 mM of glucose. These correlated with a decrease in the autolytical fragment of 50 kDa of CAPN1 and increased levels of CAST, but there were no changes in CAPN2 and CAPN10. We used a cell-free system to evaluate the effect of arsenite over CAPN1, finding that arsenite induced CAPN1 autolysis. To confirm that calpains are involved in GLUT1 trafficking and glucose uptake in lymphocytes, we generated stable CAPN1 or CAPN10 knockdowns in Jurkat cells using short hairpin RNA (shRNA). CAPN1 knockdown induced glucose uptake, while CAPN10 knockdown diminished glucose uptake, which correlated with a significant reduction of calpain activity after the pulse with 11.1 mM of glucose. These data showed that CAPN10 was responsible for the induction of calpain activity after the challenge with 11.1 mM of glucose and that CAPN1 and CAPN10 regulate glucose uptake in lymphocytes. Altogether, our results suggest that arsenite impairs GLUT1 trafficking and function through calpain dysregulation.

Role of calpain-10 in the development of diabetes mellitus and its complications

Calpain activity has been implicated in several cellular processes such as cell signaling, apoptosis, exocytosis, mitochondrial metabolism and cytoskeletal remodeling. Evidence has indicated that the impairment of calpain expression and the activity of different calpain family members are involved in diverse pathologies. Calpain-10 has been implicated in the development of type 2 diabetes, and polymorphisms in the CAPN10 gene have been associated with an increased risk of developing this disease. The present work focused on the molecular biology of calpain-10, supporting its key participation in glucose metabolism. Current knowledge regarding the role of calpain-10 in the development of type 2 diabetes mellitus and diabetes-related diseases is additionally reviewed.

Glucose Measurement by Affinity Sensor and Pulsed Measurements of Fluidic Resistances: Proof of Principle

Affinity sensors for glucose are based on a different measuring principle than the commercially available amperometric needle type sensors: reversible affinity interaction of glucose with specific receptors is the primary recognition mechanism instead of an enzymatic glucose oxidation. A novel pulsed-flow micro-fluidic system was used to characterize first the viscosity of a sensitive liquid containing the glucose receptor Concanavalin A and dextran and in a second approach to characterize the geometry of a fluidic resistance. In the viscometric sensor, glucose of the sensitive liquid is equilibrated, while passing through a dialysis chamber, with the surrounding medium. With the membrane flow sensor, the viscosity of the liquid remains constant but the pores of the flow-resisting membrane contain a swellable hydrogel affecting the width of the pores. Two types of hydrogel were tested with the membrane flow sensor; one is highly sensitive to pH and salt concentration, the other contains receptors of phenyl boronic acids to obtain sensitivity to glucose. The viscometric affinity sensor (first approach) showed a linear response over 0 to 30 mmol/L glucose concentration range. The disturbing effect of air bubbles could be compensated for. The sensing proof of principle of the second approach could be demonstrated by its linear response to different saline concentrations; however, the glucose-sensitive membrane developed showed only a small response to glucose. Glucose monitoring based on this pulsed flow measuring principle offers interesting alternatives for the development of CGM systems with different options for the glucose sensing part.

Arsenic exposure and calpain-10 polymorphisms impair the function of pancreatic beta-cells in humans: a pilot study of risk factors for T2DM

The incidence of type 2 diabetes mellitus (T2DM) is increasing worldwide and diverse environmental and genetic risk factors are well recognized. Single nucleotide polymorphisms (SNPs) in the calpain-10 gene (CAPN-10), which encodes a protein involved in the secretion and action of insulin, and chronic exposure to inorganic arsenic (iAs) through drinking water have been independently associated with an increase in the risk for T2DM. In the present work we evaluated if CAPN-10 SNPs and iAs exposure jointly contribute to the outcome of T2DM. Insulin secretion (beta-cell function) and insulin sensitivity were evaluated indirectly through validated indexes (HOMA2) in subjects with and without T2DM who have been exposed to a gradient of iAs in their drinking water in northern Mexico. The results were analyzed taking into account the presence of the risk factor SNPs SNP-43 and -44 in CAPN-10. Subjects with T2DM had significantly lower beta-cell function and insulin sensitivity. An inverse association was found between beta-cell function and iAs exposure, the association being more pronounced in subjects with T2DM. Subjects without T2DM who were carriers of the at-risk genotype SNP-43 or -44, also had significantly lower beta-cell function. The association of SNP-43 with beta-cell function was dependent on iAs exposure, age, gender and BMI, whereas the association with SNP-44 was independent of all of these factors. Chronic exposure to iAs seems to be a risk factor for T2DM in humans through the reduction of beta-cell function, with an enhanced effect seen in the presence of the at-risk genotype of SNP-43 in CAPN-10. Carriers of CAPN-10 SNP-44 have also shown reduced beta-cell function.

Genetics of adipose tissue biology

Adipose tissue morphology and release of free fatty acids, as well as peptide hormones, are believed to contribute to obesity and related metabolic disorders. These adipose tissue phenotypes are influenced by adiposity, but there is also a strong hereditary impact. Polymorphisms in numerous adipose-expressed genes have been evaluated for association with adipocyte and clinical phenotypes. In our opinion, some results are convincing. Thus ADRB2 and GPR74 genes are associated with adipocyte lipolysis, GPR74 also with BMI; PPARG and SREBP1, which promote adipogenesis and lipid storage, are associated with T2D and possible adiposity; ADIPOQ and ARL15 are associated with circulating levels of adiponectin, ARL15 also with coronary heart disease. We anticipate that the use of complementary approaches such as expression profiling and RNAi screening, and studies of additional levels of gene regulation, that is, miRNA and epigenetics, will be important to unravel the genetics of adipose tissue function.

Variants within the calpain-10 gene and relationships with type 2 diabetes (T2DM) and T2DM-related traits among Tunisian Arabs

BACKGROUND

Common variations in the calpain 10 (CAPN10) gene variants UCSNP-43, UCSNP-19 and UCSNP-63, and the 112/121 diplotype, are associated with an increased risk of type 2 diabetes (T2DM) and T2DM-related traits.

METHODS

The association of UCSNP-43, -19 and -63 CAPN10 SNPs with T2DM was assessed in 917 Tunisian T2DM patients and 748 ethnically matched non-diabetic controls. CAPN10 genotyping was done by PCR-RFLP.

RESULTS

Significant differences in UCSNP-19 MAF, but not UCSNP-43 or -63, and genotype distribution were seen between patients and controls. Heterogeneity in UCSNP-19, but not UCSNP-43 and -63, genotype distribution was noted according to geographical origin. Obesity was associated with UCSNP-19, while raised fasting glucose was associated with UCSNP-63, and increased HDL was associated with UCSNP-43. Enrichment of homozygous UCSNP-19 2/2 was seen in overweight and obese compared with lean patients; logistic-regression analyses demonstrated a positive association of the 2/2 genotype with overweight [P=0.003; OR (95% CI)=2.07 (1.28-3.33)] and obese [P=0.021; OR (95% CI)=1.83 (1.10-3.07)] patients. Of the six CAPN10 haplotypes identified, significant enrichment of only haplotype 111 was seen in T2DM patients [Pc=0.034; OR (95% CI)=1.22 (1.06-1.41)], while the frequency of all identified CAPN10 diplotypes, including the high-risk 112/121, was comparable between patients and controls.

CONCLUSION

While CAPN10 UCSNP-19 SNP and haplotype 111 contribute to the risk of T2DM in Tunisian subjects, no significant association between CAPN10 diplotypes and T2DM was demonstrated.

Calpains and their multiple roles in diabetes mellitus

Type 2 diabetes mellitus (T2DM) can lead to death without treatment and it has been predicted that the condition will affect 215 million people worldwide by 2010. T2DM is a multifactorial disorder whose precise genetic causes and biochemical defects have not been fully elucidated, but at both levels, calpains appear to play a role. Positional cloning studies mapped T2DM susceptibility to CAPN10, the gene encoding the intracellular cysteine protease, calpain 10. Further studies have shown a number of noncoding polymorphisms in CAPN10 to be functionally associated with T2DM while the identification of coding polymorphisms, suggested that mutant calpain 10 proteins may also contribute to the disease. Here we review recent studies, which in addition to the latter enzyme, have linked calpain 5, calpain 3, and its splice variants, calpain 2 and calpain 1 to T2DM-related metabolic pathways along with T2DM-associated phenotypes, such as obesity and impaired insulin secretion, and T2DM-related complications, such as epithelial dysfunction and diabetic cataract.

Calpain-10 variants and haplotypes are associated with polycystic ovary syndrome in Caucasians

PCOS is known to be associated with an increased risk of T2DM and has been proposed to share a common genetic background with T2DM. Recent studies suggest that the Calpain-10 gene (CAPN10) is an interesting candidate gene for PCOS susceptibility. However, contradictory results were reported concerning the contribution of certain CAPN10 variants, especially of UCSNP-44, to genetic predisposition to T2DM, hirsutism, and PCOS. By means of MALDI-TOF MS technique, we genotyped an expanded single nucleotide polymorphism panel, including the CAPN10 UCSNP-44, -43, -56, ins/del-19, -110, -58, -63, and -22 in a sample of 146 German PCOS women and 606 population-based controls. Statistical analysis revealed an association between UCSNP-56 and susceptibility to PCOS with an odds ratio (OR) of 2.91 (95% CI=1.51-5.61) for women carrying an AA genotype compared with GG. As expected, the 22-genotype of the ins/del-19 variant, which is in high linkage disequilibrium (r2=0.98) with UCSNP-56, was also significantly associated (OR=2.98, 95% CI=1.55-5.73). None of the additionally tested variants alone showed any significant association with PCOS. A meta-analysis including our study (altogether 623 PCOS cases and 1,224 controls) also showed significant association only with ins/del-19. The most common haplotype TGG3AGCA was significantly associated with a lower risk for PCOS (OR=0.487, P=0.0057). In contrast, the TGA2AGCA haplotype was associated with an increased risk for PCOS (OR=3.557, P=0.0011). By investigating a broad panel of CAPN10 variants, our results pointed to an allele dose-dependent association of UCSNP-56 and ins/del-19 with PCOS.

Common polymorphisms of calpain-10 are associated with abdominal obesity in subjects at high risk of type 2 diabetes

AIMS/HYPOTHESIS

The mechanisms by which the calpain-10 gene (CAPN10) affects the risk of type 2 diabetes are unclear. Therefore, we investigated the effects of four polymorphisms in CAPN10 (single nucleotide polymorphism [SNP]-43, SNP-44, Insertion/Deletion [Indel]-19 and SNP-63) on insulin secretion, insulin action and abdominal fat distribution in offspring of patients with type 2 diabetes.

SUBJECTS AND METHODS

Insulin secretion was determined by an IVGTT, insulin action by the hyperinsulinaemic-euglycaemic clamp and abdominal fat distribution by computed tomography in 158 non-diabetic offspring (age 34.9+/-6.3 years [mean+/-SD], BMI 26.2+/-4.9 kg/m(2)) of type 2 diabetic patients.

RESULTS

SNP-43 (p=0.009 over the three genotypes, adjusted for age, sex, BMI and family relationship) and haplotypes carrying the A allele of SNP-43 were associated with intra-abdominal fat area. The A allele of SNP-43 was associated with intra-abdominal fat area in men (p=0.014) but not in women. SNP-44, InDel-19 and SNP-63 were not associated with intra-abdominal fat area or insulin action. Furthermore, we demonstrated in a separate sample of middle-aged men (n=234) who had a history of type 2 diabetes in first-degree relatives that the A allele of SNP-43 was associated with a large waist circumference, and high insulin levels in an OGTT.

CONCLUSIONS/INTERPRETATION

SNP-43 of CAPN10 may contribute to the risk of diabetes by regulating abdominal obesity in subjects with high risk of type 2 diabetes.

Calpain-10: from genome search to function

Calpain-10 (CAPN10) is the first diabetes gene to be identified through a genome scan. Many investigators, but not all, have subsequently found associations between CAPN10 polymorphism and type 2 diabetes (T2D) as well as insulin action, insulin secretion, aspects of adipocyte biology and microvascular function. However, this has not always been with the same single nucleotide polymorphism (SNP) or haplotype or the same phenotype, suggesting that there might be more than one disease-associated CAPN10 variant and that these might vary between ethnic groups and the phenotype under study. Our understanding of calpain-10 physiological action has also been greatly augmented by our knowledge of the calpain family domain structure and function, and the relationship between calpain-10 and other calpains is discussed here. Both genetic and functional data indicates that calpain-10 has an important role in insulin resistance and intermediate phenotypes, including those associated with the adipocyte. In this regard, emerging evidence would suggest that calpain-10 facilitates GLUT4 translocation and acts in reorganization of the cytoskeleton. Calpain-10 is also an important molecule in the beta-cell. It is likely to be a determinant of fuel sensing and insulin exocytosis, with actions at the mitochondria and plasma membrane respectively. We postulate that the multiple actions of calpain-10 may relate to its different protein isoforms. In conclusion, the discovery of calpain-10 by a genetic approach has identified it as a molecule of importance to insulin signaling and secretion that may have relevance to the future development of novel therapeutic targets for the treatment of T2D.

Calpain 10 and type 2 diabetes: are we getting closer to an explanation?

PURPOSE OF REVIEW

A variation in the gene encoding the cysteine protease calpain 10 (CAPN10) was recently linked and associated with type 2 diabetes by positional cloning. This positional cloning was a follow-up investigation to the identification of a diabetes-linked region on human chromosome 2 identified by genome-wide scanning a few years earlier. In this paper we give a general background on the genetic studies performed on CAPN10 to date, and review the most recent studies on the functional role of calpain 10.

RECENT FINDING

A haplotype or haplotype combination comprising three intronic single nucleotide polymorphisms (UCSNP-43, 19, and 63) were associated with a threefold increased risk of type 2 diabetes in the population in which linkage was first found. Another polymorphism, UCSNP-44, which is in linkage disequilibrium with a coding single-nucleotide polymorphism (Thr504Ala), has subsequently been associated with type 2 diabetes in extensive meta-analyses. Meanwhile, initial studies probing the possible role of calpain-10, completely unknown at the time, are now being pursued, both in isolated cells and humans.

SUMMARY

The positional cloning of CAPN10 as a candidate gene for type 2 diabetes has been particularly fruitful. Not only has it identified an important and surprising piece of the puzzle underlying the development of diabetes, but it has also modelled and paved the way for investigations concerning complex genetic diseases other than type 2 diabetes.

GLUT4 expression in 3T3-L1 adipocytes is repressed by proteasome inhibition, but not by inhibition of calpains

Because of recent studies showing linkage of type 2 diabetes with the calpain 10 gene, we investigated the ability of calpains to regulate GLUT4 expression in 3T3-L1 adipocytes. Treatment of 3T3-L1 adipocytes with the calpain inhibitor ALLN significantly decreased the mRNA and protein expression of GLUT4. GLUT4 expression was not affected by treatment with the more selective calpain inhibitors PD150606, calpeptin, or a calpastatin peptide. In contrast, treatment with the proteasome inhibitors lactacystin or MG132 repressed GLUT4 mRNA level to 35% (10 microM lactacystin) and 12% (10 microM MG132) of control levels. Therefore, the expression of GLUT4 in 3T3-L1 adipocytes was repressed by proteasome inhibition, but not by inhibition of calpains; the effect of ALLN was due to its ability to inhibit proteasome function, rather than its action to inhibit calpains. Concomitant with the repression of GLUT4 mRNA levels, proteasome inhibition decreased GLUT4 protein levels in 3T3-L1 adipocytes. The decrease in GLUT4 expression occurred at the transcriptional level, as treatment with proteasome inhibitors decreased GLUT4 transcription measured by a nuclear run-on assay. Thus, these data demonstrate a new pathway for the regulation of GLUT4 expression that involves proteasomal degradation of factors that regulate GLUT4 expression.

Calpain-10 gene polymorphisms and type 2 diabetes in West Africans: the Africa America Diabetes Mellitus (AADM) Study

PURPOSE

To investigate whether the three single nucleotide polymorphisms (SNPs), SNP-43, -56, and -63 of CAPN10 were associated with type 2 diabetes in a West African cohort.

METHODS

A total of 347 diabetic subjects and 148 unaffected controls from four ethnic groups in two West African countries were enrolled in this study. After genotyping three SNPs of CAPN10 and one SNP from CYP19, the allele, genotype, and haplotype frequencies as well as the odds ratios were calculated to test their association with type 2 diabetes.

RESULTS

None of the alleles or genotypes was associated with type 2 diabetes. Although statistical analysis indicated that haplotype 221 was associated with type 2 diabetes (OR, 3.765; 95% CI, 1.577-8.989) in the two ethnic groups of Nigeria, the same haplotype did not show any association with type 2 diabetes in the two ethnic groups in Ghana (OR, 0.906; 95% CI, 0.322-2.552).

CONCLUSION

Considering the relatively low frequency of haplotype 221 and that none of the haplotypes including 221 was associated with any of the diabetes-related quantitative traits tested, it is concluded that SNP-43, -56, and -63 of the CAPN10 gene variants may play a limited role in the risk of type 2 diabetes risks in this cohort of West Africans.

Are variants in the CAPN10 gene related to risk of type 2 diabetes? A quantitative assessment of population and family-based association studies

The calpain-10 gene (CAPN10) on chromosome 2q37.3 was the first candidate gene for type 2 diabetes (T2D) identified through a genomewide screen and positional cloning. One polymorphism (UCSNP-43: G-->A) and a specific haplotype combination defined by three polymorphisms (UCSNP-43, -19, and -63) were linked to an increased risk of T2D in several populations. To quantitatively assess the collective evidence for the effects of CAPN10 on risk of T2D, we conducted a meta-analysis of both population-based and family-based association studies. We retrieved data from the MEDLINE, PubMed, and Online Mendelian Inheritance in Man databases, as well as from other relevant reports and abstracts published up to July 2003. From a total of 26 studies with primary data (21 population-based studies: 5,013 cases and 5,876 controls; 5 family-based studies: 487 parent-offspring trios), we developed a summary database that contains variables of study design, study population/ethnicity, specific polymorphisms and haplotype combinations in CAPN10, and diabetes-related metabolic phenotypes. For population-based studies, we used both fixed-effects and random-effects models to calculate the pooled odds ratio (OR) and 95% confidence interval (CI) for the associations of CAPN10 genotypes with the risk of T2D. We also calculated weighted mean differences for the associations between CAPN10 and diabetes-related quantitative traits. Under either an additive or a dominant effect model, we found no statistically significant relation between CAPN10 genotypes in the UCSNP-43 locus and T2D risk. However, under a recessive model, individuals homozygous for the common G allele had a statistically significant 19% higher risk of T2D than carriers of the A allele (OR 1.19; 95% CI 1.07-1.33). The association between the 112/121 haplotype combination and T2D risk appeared to be overestimated by several initial small studies with positive findings (OR 1.38; 95% CI 1.04-1.84). After we removed these initial studies, this association became nonsignificant (OR 1.11; 95% CI 0.91-1.35). Moreover, we found no evidence for the associations between the UCSNP-43 G/G genotype and the 112/121 haplotype combination and metabolic phenotypes. Our meta-analysis of family-based studies showed only an overtransmission of the rare allele C in UCSNP-44 from heterozygous parents to their affected offspring with T2D. Our analysis indicates that inadequate statistical power, racial/ethnic differences in frequencies of alleles, haplotypes and haplotype combinations, potential gene-gene or gene-environment interactions, publication bias, and multiple hypothesis testing may contribute to the significant heterogeneity in previous studies of CAPN10 and T2D. Our findings also suggest that both large-scale, well-designed association studies and functional studies are warranted to either reliably confirm or conclusively refute the initial hypothesis regarding the role of CAPN10 in T2D risk.

Linkage of calpain 10 to type 2 diabetes: the biological rationale

The follow-up studies to the original report of association of variation at calpain 10 (CAPN10) with type 2 diabetes in the Mexican-American population of Starr County, Texas, encompass a broad range of science. There are association studies on genetic variation at CAPN10 in different human populations over a range of phenotypes related to type 2 diabetes, physiological studies on the biological functions of calpain proteases, and evolutionary studies on CAPN10 and the NIDDM1 region. We review here the studies published to date on CAPN10, as well as the latest findings from positional cloning studies on a number of other complex disorders. Collectively, these studies provide perspective on the challenges of moving from the linkage mapping and positional cloning studies on which we have been focused to an understanding of the biology shaping the relationship of genotype to phenotype at loci influencing susceptibility to complex disorders like type 2 diabetes.

Calpain 10 as a Predictive Gene for Type 2 Diabetes: Evidence from a Novel Screening System Using White Blood Cells of Otsuka Long-Evans Tokushima Fatty (OLETF) Rats

The mRNA expression of type 2 diabetes-related genes in white blood cells (WBC) was examined before and after onset in Otsuka Long-Evans Tokushima Fatty (OLETF) rat. The level of the calpain 10 (CAPN10) transcript was significantly decreased compared to control animals in WBC before and after onset. Significant decreases in this gene expression were also found in the major insulin-target tissues as well as WBC before onset. These results suggest that gene expression in WBC could be a useful screening system for predicting the incidence of type 2 diabetes before onset in OLETF rats, and that CAPN10 represents a potential candidate gene for predicting type 2 diabetes in human.

Hypoglycemia warning signal and glucose sensors: requirements and concepts

Hypoglycemia is the most feared side effect of diabetes therapy with blood glucose-lowering agents. The fear of hypoglycemia often contributes to poor metabolic control of patients with diabetes. Therefore, integration of a hypoglycemia warning signal into continuous glucose monitoring systems represents an important additional help for patients with diabetes. The warning signal can be triggered at a preset level based on the current glucose values (as provided with the presently available glucose monitoring systems) or on prospective trend analysis offering the possibility to predict the risk of a hypoglycemic event in an anticipatory manner. Using the approach of a "Finite State Machine," such a more advanced warning system can completely be described as a finite collection of four states and possible transitions in-between. Most of the currently available glucose monitoring systems measure glucose in the interstitial fluid (ISF) of the dermal or subcutaneous tissue but are calibrated to blood glucose levels. This requires a number of factors to be taken into account: precision and accuracy of the glucose measurements, physiological and physical lag time, and calibration of the glucose monitoring system. From our point of view, the analytical performance of the system should be such that the majority of all hypoglycemic episodes are correctly diagnosed (>75%). Inconsistent findings regarding physiological discrepancies between blood and ISF glucose, which usually are described as a physiological lag time, range from some seconds up to 15 min. They can be observed especially during dynamic blood glucose changes (>3 mg/dL/min) and may represent major challenges for the development of a reliable hypoglycemia warning signal. In addition to possible physiological time lags, device-inherent physical lag times must be considered when selecting the threshold for the warning signal. Despite these problems, most probably all patients with diabetes who are treated with blood glucose-lowering agents will benefit from such a system since their safety and quality of life can be greatly improved, including an optimized metabolic control and lowered diabetes-related mortality. The benefit will be greatest for patients with hypoglycemia unawareness or impaired perception of hypoglycemic symptoms. The risks related to the use of a hypoglycemia warning signal seem to be low if certain precautionary measures are taken. In any case, additional clinical-experimental studies in healthy subjects as well as long-term clinical studies in diabetic patients are necessary to further evaluate the efficacy, benefits, and risks of different hypoglycemia warning concepts implemented in the different continuous glucose monitoring systems.

Glucose sensors and the alternate site testing-like phenomenon: relationship between rapid blood glucose changes and glucose sensor signals

In the last few years blood glucose meters have been developed allowing glucose measurements in capillary blood samples collected at sites other than the fingertips. The main reason for establishing this so-called alternate site testing (AST) was to sample blood from locations with reduced pain perception. It is well known that capillary blood glucose is closely correlated to systemic (i.e., arterial) glucose levels and that under steady-state conditions, glucose values measured in blood samples collected from alternate sites are virtually identical to those collected from the fingertip. However, during rapid changes in blood glucose levels, glucose concentrations in capillary blood samples from the fingertips can differ considerably in both domains (time and concentration) from those determined in capillary blood from alternate sites (i.e., the so-called AST phenomenon). Such differences can have serious clinical consequences (e.g., risky delays in hypoglycemia detection). There is evidence that all skin sites exhibiting a reduced blood flow (in comparison with the fingertip) within the superficial skin layers are prone to this AST phenomenon. Nearly all glucose sensors having been developed so far or being currently under development measure glucose levels at alternate sites and also in another compartment [e.g., interstitial fluid (ISF)] than blood. So, in principle they might be prone to an AST-like phenomenon (i.e., rapid changes in systemic blood glucose levels may also result in delayed ISF glucose readings). Our knowledge about the impact of an AST-like phenomenon on the performance of glucose monitoring systems is presently very limited. Glucose kinetics in the different compartments during dynamic systemic blood glucose changes have not been fully elucidated yet. If an AST-like phenomenon plays a role with glucose sensors should therefore be studied. Depending on the measurement technology used for the individual type of glucose monitoring system probably this phenomenon has a variable impact on the results obtained.

Bases Genéticas do Diabetes Mellitus Tipo 2

A patogênese do diabetes mellitus tipo 2 (DM2) é complexa, associando fatores genéticos e fatores ambientais. A hiperglicemia é secundária à combinação de defeitos tanto na sensibilidade à insulina quanto na disfunção das células beta-pancreáticas. Vários estudos estabeleceram claramente a importância dos fatores genéticos na predisposição ao DM2. No momento, conhecemos alguns genes implicados em formas monogênicas de diabetes (MODY, diabetes mitocondrial). No entanto, nas formas mais comuns da doença de caráter poligênico, conhecemos apenas poucos genes que são associados à doença de uma forma reprodutível nos diferentes grupos populacionais estudados. Cada um destes poligenes apresenta um papel isolado muito pequeno, atuando na modulação de fenótipos associados ao diabetes. Nestas formas tardias poligênicas de DM2 é evidente a importância dos fatores ambientais que modulam a expressão clínica da doença. Nesta revisão abordamos os avanços mais relevantes das bases genéticas do DM2.