Optimizing clinical outcomes resulting from glucose-lowering therapies in type 2 diabetes: increased confidence about the DPP-4 inhibitors and continued concerns regarding sulphonylureas and exogenous insulin

Scientific independence and objectivity: many questions linger about treatment of type 2 diabetes, such as scientific study design, optimal glucose control and the safety of injecting exogenous insulin

Whilst clinical guidelines exist for the treatment of people with type 2 diabetes, many underlying assumptions are still not qualified by convincing evidence. In this commentary, it is argued that fundamental issues still cloud clinical practice, such as biases in the design of clinical studies, the association between glucose control & clinical outcomes, and the safety of exposure to exogenous insulin and other glucose-lowering drugs. Relevant scientific evidence and alternative opinions about important issues continue to be largely ignored, and no effort has been made to resolve these questions. This may have had serious consequences, such as stifling innovation because there are no further benefits to be achieved in relation to glucose control.

Insulin Therapy Increases Cardiovascular Risk in Type 2 Diabetes

Insulin therapy increased cardiovascular (CV) risk and mortality among type 2 diabetes (T2D) patients in several recently reported clinical outcomes trials. To assess whether this association is causative or coincidental, PubMed searches were used to query the effects of insulin therapy for T2D on CV health and longevity from large-scale outcomes trials, meta-analyses, and patient registry studies, as well as basic research on insulin's direct and pleiotropic actions. Although several old studies provided conflicting results, the majority of large observational studies show strong dose-dependent associations for injected insulin with increased CV risk and worsened mortality. Insulin clearly causes weight gain, recurrent hypoglycemia, and, other potential adverse effects, including iatrogenic hyperinsulinemia. This over-insulinization with use of injected insulin predisposes to inflammation, atherosclerosis, hypertension, dyslipidemia, heart failure (HF), and arrhythmias. These associations support the findings of large-scale evaluations that strongly suggest that insulin therapy has a poorer short- and long-term safety profile than that found to many other anti-T2D therapies. The potential adverse effects of insulin therapy should be weighed against proven CV benefits noted for select other therapies for T2D as reported in recent large randomized controlled trials.

New forms of insulin and insulin therapies for the treatment of type 2 diabetes

Insulin is a common treatment option for many patients with type 2 diabetes, and is generally used late in the natural history of the disease. Its injectable delivery mode, propensity for weight gain and hypoglycaemia, and the paucity of trials assessing the risk-to-safety ratio of early insulin use are major shortcomings associated with its use in patients with type 2 diabetes. Development of new insulins-such as insulin analogues, including long-acting and short-acting insulins-now provide alternative treatment options to human insulin. These novel insulin formulations and innovative insulin delivery methods, such as oral or inhaled insulin, have been developed with the aim to reduce insulin-associated hypoglycaemia, lower intraindividual pharmacokinetic and pharmacodynamic variability, and improve imitation of physiological insulin release. Availability of newer glucose-lowering drugs (such as glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, and sodium-glucose co-transporter-2 inhibitors) also offers the opportunity for combination treatment; the results of the first trials in this area of research suggest that such treatment might lead to use of reduced insulin doses, less weight gain, and fewer hypoglycaemic episodes than insulin treatment alone. These and future developments will hopefully offer better opportunities for individualisation of insulin treatment for patients with type 2 diabetes.

Glucose-lowering with exogenous insulin monotherapy in type 2 diabetes: dose association with all-cause mortality, cardiovascular events and cancer

AIMS

To evaluate the association between insulin exposure and all-cause mortality, incident major adverse cardiovascular events (MACE) and incident cancer in people with type 2 diabetes treated with insulin monotherapy.

METHODS

For this retrospective study, people with type 2 diabetes who progressed to insulin monotherapy from the year 2000 were identified from the UK Clinical Practice Research Datalink. The risks of progression to serious adverse outcomes were compared using Cox proportional hazards models. In the main analysis, insulin exposure was introduced into the model as prescribed international units per kilogram per day, as a cumulative, continuous, annually updated, time-dependent covariable.

RESULTS

A total of 6484 subjects with type 2 diabetes who progressed to treatment with insulin monotherapy from the year 2000 onwards were followed for a mean of 3.3 years. The event numbers were as follows: deaths, n = 1110; incident MACE, n = 342; incident cancers, n = 382. Unadjusted event rates were 61.3 deaths per 1000 person-years, 26.4 incident MACE per 1000 person-years and 24.6 incident cancers per 1000 person-years. The adjusted hazard ratios in relation to 1-unit increases in insulin dose were 1.54 [95% confidence interval (CI) 1.32-1.78] for all-cause mortality, 1.37 (95% CI 1.05-1.81) for MACE and 1.35 (95% CI 1.04-1.75) for cancer.

CONCLUSIONS

There was an association between increasing exogenous insulin dose and increased risk of all-cause mortality, MACE and cancer in people with type 2 diabetes. The limitations of observational studies mean that this should be further investigated using an interventional study design.