Diabetes, colorectal cancer and cyclooxygenase 2 inhibition

Diabetes and Colorectal Cancer Risk: Clinical and Therapeutic Implications

Several epidemiological studies have identified diabetes as a risk factor for colorectal cancer (CRC). The potential pathophysiological mechanisms of this association include hyperinsulinemia, insulin-like growth factor (IGF) axis, hyperglycemia, inflammation induced by adipose tissue dysfunction, gastrointestinal motility disorder, and impaired immunological surveillance. Several studies have shown that underlying diabetes adversely affects the prognosis of patients with CRC. This review explores the novel anticancer agents targeting IGF-1R and receptor for advanced glycation end products (RAGE), both of which play a vital role in diabetes-induced colorectal tumorigenesis. Inhibitors of IGF-1R and RAGE are expected to become promising therapeutic choices, particularly for CRC patients with diabetes. Furthermore, hypoglycemic therapy is associated with the incidence of CRC. Selection of appropriate hypoglycemic agents, which can reduce the risk of CRC in diabetic patients, is an unmet issue. Therefore, this review mainly summarizes the current studies concerning the connections among diabetes, hypoglycemic therapy, and CRC as well as provides a synthesis of the underlying pathophysiological mechanisms. Our synthesis provides a theoretical basis for rational use of hypoglycemic therapies and early diagnosis and treatment of diabetes-related CRC.

Progress in understanding of relationship between diabetes and colorectal cancer

Several epidemiological studies have suggested that diabetes is closely associated with an increased risk of colorectal cancer and diabetes could be regarded as an independent risk factor for colorectal cancer. Potential pathophysiological mechanisms connecting diabetes and colorectal cancer include hyperglycemia, hyperinsulinemia, and insulin-like growth factor axis, chronic inflammation and oxidative stress, gastrointestinal motility disorder, and impaired immunological surveillance. Meanwhile, multiple studies have revealed that diabetes is negatively related to the prognosis of patients with colorectal cancer. This review mainly summarizes the current studies concerning the linkages between diabetes and colorectal cancer and the underlying pathophysiological mechanisms, so as to provide a theoretical basis for rational use of antidiabetic drugs and early diagnosis of diabetes-related colorectal cancer.

Association between markers of glucose metabolism and risk of colorectal cancer

OBJECTIVES

Independent epidemiological studies have evaluated the association between markers of glucose metabolism (including fasting glucose, fasting insulin, homeostasis model of risk assessment-insulin resistance (HOMA-IR), glycated haemoglobin (HbA1c) and C peptide) and the risk of colorectal cancer (CRC). However, such associations have not been systematically analysed and no clear conclusions have been drawn. Therefore, we addressed this issue using a meta-analysis approach.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

PubMed and EMBASE were searched up to May 2015.

PRIMARY AND SECONDARY OUTCOME MEASURES

Either a fixed-effects or random-effects model was adopted to estimate overall ORs for the association between markers of glucose metabolism and the risk of CRC. In addition, dose-response, meta-regression, subgroup and publication bias analyses were conducted.

RESULTS

35 studies involving 25 566 patients and 5 706 361 participants were included. Higher levels of fasting glucose, fasting insulin, HOMA-IR, HbA1c and C peptide were all significantly associated with increased risk of CRC (fasting glucose, pooled OR=1.12, 95% CI 1.06 to 1.18; fasting insulin, pooled OR=1.42, 95% CI 1.19 to 1.69; HOMA-IR, pooled OR=1.47, 95% CI 1.24 to 1.74; HbA1c, pooled OR=1.22, 95% CI 1.02 to 1.47 (with borderline significance); C peptide, pooled OR=1.27, 95% CI 1.08 to 1.49). Subgroup analysis suggested that a higher HOMA-IR value was significantly associated with CRC risk in all subgroups, including gender, study design and geographic region. For the relative long-term markers, the association was significant for HbA1c in case-control studies, while C peptide was significantly associated with CRC risk in both the male group and colon cancer.

CONCLUSIONS

The real-time composite index HOMA-IR is a better indicator for CRC risk than are fasting glucose and fasting insulin. The relative long-term markers, HbA1c and C peptide, are also valid predictors for CRC risk. Considering the included case-control studies in the current analysis, more cohort studies are warranted to enhance future analysis.

Diabetes mellitus increases the risk of colorectal neoplasia: An updated meta-analysis

OBJECTIVE

Recent studies proved that patients with diabetes were at significantly higher risk of developing colorectal cancer. However, the association between diabetes mellitus and the risk of colorectal adenoma remains undefined. Thus we conducted an updated meta-analysis to identify the association between diabetes mellitus and the risk of colorectal neoplasia including adenoma and cancer.

METHODS

We conducted a search in databases including Pubmed, Web of Science, EMBASE Databases, Cochrane CENTRAL, Wanfang Data, and CNKI database. Case-control and cohort studies were included. All articles were published before January 2015 and the quality of each study was evaluated by the Newcastle-Ottawa Scale. Odds ratios (ORs) or relative risks (RRs) and its corresponding 95% confidence intervals (CIs) for each study were calculated and summary relative risk estimates with corresponding 95% CIs were generated using the random-effects model. Heterogeneity and publication bias were assessed.

RESULTS

Twenty-nine articles including ten case-control studies and nineteen cohort studies were included in this meta-analysis. In a pooled analysis of all studies, diabetes mellitus was associated with increased risk of colorectal neoplasia (RR=1.35, 95% CI=1.28-1.42). The risk increased significantly for both colorectal cancer (RR=1.37, 95% CI=1.30-1.45) and adenoma (RR=1.26, 95% CI=1.11-1.44). Subgroup analyses on study design, gender, geographical region, and type of diabetes mellitus further evidenced these findings.

CONCLUSIONS

Diabetes mellitus was associated with an increased risk of colorectal neoplasia. Not only the increased risk of colorectal cancer but also the higher risk of adenoma was identified in patients with diabetes mellitus.

Inhibitory G proteins and their receptors: emerging therapeutic targets for obesity and diabetes

The worldwide prevalence of obesity is steadily increasing, nearly doubling between 1980 and 2008. Obesity is often associated with insulin resistance, a major risk factor for type 2 diabetes mellitus (T2DM): a costly chronic disease and serious public health problem. The underlying cause of T2DM is a failure of the beta cells of the pancreas to continue to produce enough insulin to counteract insulin resistance. Most current T2DM therapeutics do not prevent continued loss of insulin secretion capacity, and those that do have the potential to preserve beta cell mass and function are not effective in all patients. Therefore, developing new methods for preventing and treating obesity and T2DM is very timely and of great significance. There is now considerable literature demonstrating a link between inhibitory guanine nucleotide-binding protein (G protein) and G protein-coupled receptor (GPCR) signaling in insulin-responsive tissues and the pathogenesis of obesity and T2DM. These studies are suggesting new and emerging therapeutic targets for these conditions. In this review, we will discuss inhibitory G proteins and GPCRs that have primary actions in the beta cell and other peripheral sites as therapeutic targets for obesity and T2DM, improving satiety, insulin resistance and/or beta cell biology.

Relationship between type-2 diabetes and use of metformin with risk of colorectal adenoma in an American population receiving colonoscopy

The aim of this study is to explore the relationship between type-2 diabetes, its treatments (Use of metformin) and the development of colorectal adenoma. Colonoscopy reports from a total of 66 endoscopists in one big hospital in midwest during 2008-2009 were reviewed. Colonoscopy findings including quality of preparation, polyp size, location, morphology, pathology and history of diabetes and metformin treatment were retrieved. Of the 7382 colonoscopy reports were reviewed, 3465 average risk patients were included in our final analysis. The pathologically proven Adenoma detection rate (ADR) in total population was 24.6 % (30.2% in Men and 19.2% in Women). Old age and male sex were significantly associated with increasing risk of colorectal adenoma. Type-2 diabetes was associated increased risk of colorectal adenoma (OD 1.35, 95% confidence interval 1.08-1.70, p=0.009). A total of 426 subjects (12.29%) had diabetes and 405 of these subjects (11.7%) had type-2 diabetes. Within diabetic patient group, people who were taking metformin have significantly lower risk of colorectal adenoma (OD 0.55, 95% confidence interval 0.34-0.87, p=0.011). Diabetic subjects have increased risk of developing colorectal adenoma. Our study also supports the beneficial effect of metformin in development of colorectal adenoma.

Diabetes mellitus and the occurrence of colorectal cancer: an updated meta-analysis of cohort studies

BACKGROUND

Recently, it has been found that diabetes patients have a higher incidence of colorectal cancer than the general population, but epidemiological studies examining a potential relationship between the two have produced inconsistent conclusions. Thus, we set out to perform a meta-analysis of cohort studies to evaluate the association between diabetes and colorectal cancer.

MATERIALS AND METHODS

Using "diabetes," "colorectal cancer," and associated key words, we performed a systematic review of published cohort studies in multiple databases, including MEDLINE, EMBASE, ISI Web of Knowledge databases, OVID, CNKI, CBMD ISC, WANFANG, and CQVIP. We then applied stringent inclusion and exclusion criteria to identify which studies to include in our analysis. STATA version 12.0 software (StataCorp., College Station, TX) was used to conduct statistical analysis, including consolidated statistics calculations, tests for heterogeneity, and publication bias evaluations.

RESULTS

We obtained a total of 532 potential articles. In accordance with our inclusion and exclusion criteria, we selected 29 articles for the meta-analysis. The analysis of extracted information indicated that diabetes is a risk factor for the development of colorectal cancer (relative risk 1.22, 95% confidence interval 1.19-1.26). Subgroup analyses by control populations, regions, gender, follow-up time, and colorectal cancer site also support this finding.

CONCLUSIONS

The risk of individuals with diabetes to develop colorectal cancer is 1.22 times higher than that of individuals without diabetes. The positive association remains consistent for both men and women and for studies carried out in North America, Europe, and Asia, as well as for different follow-up times.

Diabetes and cancer: Could vitamin D provide the link?

Diabetes and cancer are common diseases that may co-exist in the same individual. There is significant evidence that patients with diabetes have increased risk of developing certain cancers, especially colorectal, pancreatic and primary hepatic cancer. There is also good evidence that low levels of vitamin D are associated with increased risk of diabetes and increased risk of colorectal, and possibly other, cancers. In this article we propose that low levels of vitamin D may increase the risk of cancer in people with diabetes and describe potential molecular pathways. We suggest that large scale randomised trials of vitamin D supplementation in patients at risk of diabetes, and in patients with established diabetes to examine the effect on cancer risk, are required.

Diabetes mellitus and the incidence of colorectal cancer: an updated systematic review and meta-analysis

AIM

The purpose of this study was to determine whether diabetes mellitus is associated with an increased risk of colorectal cancer.

METHODS

Relevant studies were identified in MEDLINE and EMBASE (up until November 1st, 2011). Inclusion criteria were original, peer-reviewed publications, with case-control and cohort studies (for studies on diabetes mellitus and colorectal cancer). Summary relative risks with 95% confidence intervals were calculated with a random-effects model.

RESULTS

Twenty-four studies including eight case-control and 16 cohort studies, with a total of 3,659,341 participants, were included in this updated systematic review and meta-analysis, and all involved diabetes mellitus and colorectal cancer risk. Meta-analysis of the 24 included studies indicated that diabetes was associated with an increased risk of colorectal cancer, compared with no diabetes (summary RR of colorectal cancer incidence = 1.26, 95% CI = 1.20-1.31), without heterogeneity between studies (P(heterogeneity) = 0.296). Sub-group analyses found that these results were consistent between case-control and cohort studies and among studies conducted in different areas. The association between diabetes and colorectal cancer incidence did not differ significantly by sex and sub-sites. Insulin therapy was also positively associated with risk of colorectal cancer (summary RR = 1.61, 95% CI 1.18-1.35), with evidence of heterogeneity between studies (P(heterogeneity) = 0.014).

CONCLUSIONS

Our findings further support a relationship between diabetes and increased risk of colon and rectal cancer in both women and men, and insulin therapy for diabetes may increase this risk.

Natural isothiocyanates: genotoxic potential versus chemoprevention

Isothiocyanates, occurring in many dietary cruciferous vegetables, show interesting chemopreventive activities against several chronic-degenerative diseases, including cancer, cardiovascular diseases, neurodegeneration, diabetes. The electrophilic carbon residue in the isothiocyanate moiety reacts with biological nucleophiles and modification of proteins is recognized as a key mechanism underlying the biological activity of isothiocyanates. The nuclear factor-erythroid-2-related factor 2 system, which orchestrates the expression of a wide array of antioxidant genes, plays a role in the protective effect of isothiocyanates against almost all the pathological conditions reported above. Recent emerging findings suggest a further common mechanism. Chronic inflammation plays a central role in many human diseases and isothiocyanates inhibit the activity of many inflammation components, suppress cyclooxygenase 2, and irreversibly inactivate the macrophage migration inhibitory factor. Due to their electrophilic reactivity, some isothiocyanates are able to form adducts with DNA and induce gene mutations and chromosomal aberrations. DNA damage has been demonstrated to be involved in the pathogenesis of various chronic-degenerative diseases of epidemiological relevance. Thus, the genotoxicity of the isothiocyanates should be carefully considered. In addition, the dose-response relationship for genotoxic compounds does not suggest evidence of a threshold. Thus, chemicals that are genotoxic pose a greater potential risk to humans than non-genotoxic compounds. Dietary consumption levels of isothiocyanates appear to be several orders of magnitude lower than the doses used in the genotoxicity studies and thus it is highly unlikely that such toxicities would occur in humans. However, the beneficial properties of isothiocyanates stimulated an increase of dietary supplements and functional foods with highly enriched isothiocyanate concentrations on the market. Whether such concentrations may exert a potential health risk cannot be excluded with certainty and an accurate evaluation of the toxicological profile of isothiocyanates should be prompted before any major increase in their consumption be recommended or their clinical use suggested.

Is diabetes a causal agent for colorectal cancer? Pathophysiological and molecular mechanisms

The possible relationship between diabetes mellitus (DM) and colorectal cancer (CRC), concerning pathophysiological and molecular mechanisms is highlighted in this review. The most recent and complete articles and developments in this particular field were thoroughly reviewed. Common risk factors, such as obesity, sedentary lifestyle, and Western diet between DM and CRC, led to the theory that DM might be a causal agent for CRC development. Various studies have connected type 2 DM and CRC, either proximal or distal, in both sexes. Additionally, chronic insulin treatment has been linked with increased colorectal tumor risk among type 2 diabetic patients. Interestingly, elevated hemoglobin A1c has been proven to be an independent predictor of aggressive clinical behavior in CRC patients. These mechanisms include the insulin-like growth factor-hyperinsulinemia theory and the participation of oncogenic intracellular signaling pathways. Furthermore, it has been proposed that Cox-2 inhibitors might have a role in decreasing the incidence of CRC. Finally, the use of statins to reduce the risk for colon cancer in patients with diabetes has remained controversial. Diabetic patients over 50 should receive counseling regarding their elevated risk for CRC, and screening colonoscopy should be recommended before initiating insulin therapy. However, there are no current guidelines, and this strategy is not yet applicable to some countries, as the corresponding risk would not allow screening colonoscopy to be adopted. There is strong evidence to indicate that DM is a causal agent for CRC development. This conclusion provides new impetus for re-evaluating CRC screening worldwide.