Pancreatic beta cell function
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| Pancreatic beta cell function | |
|---|---|
| Other names | Gβ, HOMA-Beta, IGI, SPINA-GBeta |
| Specialty | Endocrinology |
Pancreatic beta cell function (synonyms Gβ or, if calculated from fasting concentrations of insulin and glucose, HOMA-Beta or SPINA-GBeta) is one of the preconditions of euglycaemia, i.e. normal blood sugar regulation. It is defined as insulin secretory capacity, i.e. the maximum amount of insulin to be produced by beta cells in a given unit of time.
Beta cells play a paramount role in glucose homeostasis. Progressive loss of insulin secretory capacity is a key defect associated with the transition from a healthy glycaemic state to hyperglycaemia, characteristic of untreated diabetes mellitus. In type 1 diabetes mellitus and pancreatogenic diabetes beta cell destruction is a primary event from the perspective of the feedback loop. In type 2 diabetes beta cell dysfunction is an essential constituent as well,[1] but subsequent to the development of insulin resistance.[2][3] Other mechanisms, including lipotoxicity, amyloid deposition, oxidative stress, mitochondrial dysfunction, ER stress and inflammation may be involved as well.[4][3] The beta cell loss in type 2 diabetes is mainly caused by reduced beta cell number rather than size.[5] Hyperglycaemia becomes clinically significant once insulin over-secretion can no longer compensate for the degree of insulin resistance.[2][4][1]
It remains an unsolved question if impaired pancreatic beta cell function or hypersecretion of insulin represent the primary event in the pathogenesis of type 2 diabetes.[6] Both scenarios may be cause and consequence, and it has been postulated that the direction of causality depends on the respective subtype of diabetes.[6] Therefore, they may be part of a complex feedback loop involving glucose toxicity leading to a biphasic response, thereby preventing neoplastic effects of dynamical compensation by mutant takeover.[7]
Assessing beta cell function
Measuring beta-cell function is a challenge, since insulin secretory capacity cannot be readily assessed. Therefore, indirect methods of measurement have been developed. They include dynamic and static function tests.[8][9]
Single-point measurements
One-time measurements of certain hormones or metabolites provide some limited information. Examples are:
- Fasting glucose concentration
- Fasting or random C-peptide concentration
Although single-point measurements have the benefit of being convenient and inexpensive, they are generally not regareded as sufficiently informative for early diagnosis of impaired glucose homeostasis or early-stage type 1 diabetes.[10]
Dynamic function tests
Dynamic function tests for beta-cell function include:[11][12][13]
- Oral glucose tolerance testing (OGTT)
- Intravenous glucose tolerance tests (IVGTT)
- Meal tolerance tests
- Hyperglycaemic clamp
Static function tests
Static function tests for the assessment of beta-cell function comprise:[14][15]
