Angus G. Jones

Specific C-Terminal Cleavage and Inactivation of Interleukin-8 by Invasive Disease Isolates of Streptococcus pyogenes

Lethal necrotizing fasciitis caused by Streptococcus pyogenes is characterized by a paucity of neutrophils at the site of infection. Interleukin (IL)-8, which is important for neutrophil transmigration and activation, can be degraded by S. pyogenes. Blood isolates of S. pyogenes were better able to degrade human IL-8 than throat isolates. Degradation of IL-8 was the result of a single specific cleavage between 59glutamine and 60arginine within the IL-8 C-terminal alpha helix. Cleaved IL-8 reduced neutrophil activation and migration. IL-8-cleaving activity was found in partially purified supernatant of a necrotizing fasciitis isolate, and this activity was associated with an approximately 150-kDa fraction containing S. pyogenes cell envelope proteinase (SpyCEP). IL-8-cleaving activity corresponded with the presence of SpyCEP in the supernatant. Cleavage of IL-8 by S. pyogenes represents an unprecedented mechanism of immune evasion, effectively preventing IL-8 C-terminus-mediated endothelial translocation and subsequent recruitment of neutrophils.

The clinical utility of C-peptide measurement in the care of patients with diabetes

C‐peptide is produced in equal amounts to insulin and is the best measure of endogenous insulin secretion in patients with diabetes. Measurement of insulin secretion using C‐peptide can be helpful in clinical practice: differences in insulin secretion are fundamental to the different treatment requirements of Type 1 and Type 2 diabetes. This article reviews the use of C‐peptide measurement in the clinical management of patients with diabetes, including the interpretation and choice of C‐peptide test and its use to assist diabetes classification and choice of treatment. We provide recommendations for where C‐peptide should be used, choice of test and interpretation of results. With the rising incidence of Type 2 diabetes in younger patients, the discovery of monogenic diabetes and development of new therapies aimed at preserving insulin secretion, the direct measurement of insulin secretion may be increasingly important. Advances in assays have made C‐peptide measurement both more reliable and inexpensive. In addition, recent work has demonstrated that C‐peptide is more stable in blood than previously suggested or can be reliably measured on a spot urine sample (urine C‐peptide:creatinine ratio), facilitating measurement in routine clinical practice. The key current clinical role of C‐peptide is to assist classification and management of insulin‐treated patients. Utility is greatest after 3–5 years from diagnosis when persistence of substantial insulin secretion suggests Type 2 or monogenic diabetes. Absent C‐peptide at any time confirms absolute insulin requirement and the appropriateness of Type 1 diabetes management strategies regardless of apparent aetiology.

The majority of patients with long-duration type 1 diabetes are insulin microsecretors and have functioning beta cells

Fig. 2 The effect of a meal stimulus on serum C-peptide levels in participants with detectable insulin (n =54). (a) Paired fasting and mixed meal results for all patients with detectable C-peptide. Each line represents an individual patient. (b ) Results for all patients with fasting C-peptide below 30 pmol/l (n=36). Of 54 patients, 43 (80%) had a serum Table 1 Summary data for serum and urinary C-peptide results using the Roche assay

A Type 1 Diabetes Genetic Risk Score Can Aid Discrimination Between Type 1 and Type 2 Diabetes in Young Adults

OBJECTIVE With rising obesity, it is becoming increasingly difficult to distinguish between type 1 diabetes (T1D) and type 2 diabetes (T2D) in young adults. There has been substantial recent progress in identifying the contribution of common genetic variants to T1D and T2D. We aimed to determine whether a score generated from common genetic variants could be used to discriminate between T1D and T2D and also to predict severe insulin deficiency in young adults with diabetes. RESEARCH DESIGN AND METHODS We developed genetic risk scores (GRSs) from published T1D- and T2D-associated variants. We first tested whether the scores could distinguish clinically defined T1D and T2D from the Wellcome Trust Case Control Consortium (WTCCC) (n = 3,887). We then assessed whether the T1D GRS correctly classified young adults (diagnosed at 20–40 years of age, the age-group with the most diagnostic difficulty in clinical practice; n = 223) who progressed to severe insulin deficiency <3 years from diagnosis. RESULTS In the WTCCC, the T1D GRS, based on 30 T1D-associated risk variants, was highly discriminative of T1D and T2D (area under the curve [AUC] 0.88 [95% CI 0.87–0.89]; P < 0.0001), and the T2D GRS added little discrimination (AUC 0.89). A T1D GRS >0.280 (>50th centile in those with T1D) is indicative of T1D (50% sensitivity, 95% specificity). A low T1D GRS (<0.234, <5th centile T1D) is indicative of T2D (53% sensitivity, 95% specificity). Most discriminative ability was obtained from just nine single nucleotide polymorphisms (AUC 0.87). In young adults with diabetes, T1D GRS alone predicted progression to insulin deficiency (AUC 0.87 [95% CI 0.82–0.92]; P < 0.0001). T1D GRS, autoantibody status, and clinical features were independent and additive predictors of severe insulin deficiency (combined AUC 0.96 [95% CI 0.94–0.99]; P < 0.0001). CONCLUSIONS A T1D GRS can accurately identify young adults with diabetes who will require insulin treatment. This will be an important addition to correctly classifying individuals with diabetes when clinical features and autoimmune markers are equivocal.

Markers of β-Cell Failure Predict Poor Glycemic Response to GLP-1 Receptor Agonist Therapy in Type 2 Diabetes

OBJECTIVE To assess whether clinical characteristics and simple biomarkers of β-cell failure are associated with individual variation in glycemic response to GLP-1 receptor agonist (GLP-1RA) therapy in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS We prospectively studied 620 participants with type 2 diabetes and HbA1c ≥58 mmol/mol (7.5%) commencing GLP-1RA therapy as part of their usual diabetes care and assessed response to therapy over 6 months. We assessed the association between baseline clinical measurements associated with β-cell failure and glycemic response (primary outcome HbA1c change 0–6 months) with change in weight (0–6 months) as a secondary outcome using linear regression and ANOVA with adjustment for baseline HbA1c and cotreatment change. RESULTS Reduced glycemic response to GLP-1RAs was associated with longer duration of diabetes, insulin cotreatment, lower fasting C-peptide, lower postmeal urine C-peptide–to–creatinine ratio, and positive GAD or IA2 islet autoantibodies (P ≤ 0.01 for all). Participants with positive autoantibodies or severe insulin deficiency (fasting C-peptide ≤0.25 nmol/L) had markedly reduced glycemic response to GLP-1RA therapy (autoantibodies, mean HbA1c change −5.2 vs. −15.2 mmol/mol [−0.5 vs. −1.4%], P = 0.005; C-peptide <0.25 nmol/L, mean change −2.1 vs. −15.3 mmol/mol [−0.2 vs. −1.4%], P = 0.002). These markers were predominantly present in insulin-treated participants and were not associated with weight change. CONCLUSIONS Clinical markers of low β-cell function are associated with reduced glycemic response to GLP-1RA therapy. C-peptide and islet autoantibodies represent potential biomarkers for the stratification of GLP-1RA therapy in insulin-treated diabetes.

Urine C-Peptide Creatinine Ratio Is a Noninvasive Alternative to the Mixed-Meal Tolerance Test in Children and Adults With Type 1 Diabetes

OBJECTIVE Stimulated serum C-peptide (sCP) during a mixed-meal tolerance test (MMTT) is the gold standard measure of endogenous insulin secretion, but practical issues limit its use. We assessed urine C-peptide creatinine ratio (UCPCR) as an alternative. RESEARCH DESIGN AND METHODS Seventy-two type 1 diabetic patients (age of diagnosis median 14 years [interquartile range 10–22]; diabetes duration 6.5 [2.3–32.7]) had an MMTT. sCP was collected at 90 min. Urine for UCPCR was collected at 120 min and following a home evening meal. RESULTS MMTT 120-min UCPCR was highly correlated to 90-min sCP (r = 0.97; P < 0.0001). UCPCR ≥0.53 nmol/mmol had 94% sensitivity/100% specificity for significant endogenous insulin secretion (90-min sCP ≥0.2 nmol/L). The 120-min postprandial evening meal UCPCR was highly correlated to 90-min sCP (r = 0.91; P < 0.0001). UCPCR ≥0.37 nmol/mmol had 84% sensitivity/97% specificity for sCP ≥0.2 nmol/L. CONCLUSIONS UCPCR testing is a sensitive and specific method for detecting insulin secretion. UCPCR may be a practical alternative to serum C-peptide testing, avoiding the need for inpatient investigation.

Urine C-peptide creatinine ratio is an alternative to stimulated serum C-peptide measurement in late-onset, insulin-treated diabetes.

Diabet. Med. 28, 1034–1038 (2011)

Can clinical features be used to differentiate type 1 from type 2 diabetes? A systematic review of the literature

Objective Clinicians predominantly use clinical features to differentiate type 1 from type 2 diabetes yet there are no evidence-based clinical criteria to aid classification of patients. Misclassification of diabetes is widespread (7–15% of cases), resulting in patients receiving inappropriate treatment. We sought to identify which clinical criteria could be used to discriminate type 1 and type 2 diabetes. Design Systematic review of all diagnostic accuracy studies published since 1979 using clinical criteria to predict insulin deficiency (measured by C-peptide). Data sources 14 databases including: MEDLINE, MEDLINE in Process and EMBASE. The search strategy took the form of: (terms for diabetes) AND (terms for C-Peptide). Eligibility criteria Diagnostic accuracy studies of any routinely available clinical predictors against a reference standard of insulin deficiency defined by cut-offs of C-peptide concentrations. No restrictions on race, age, language or country of origin. Results 10 917 abstracts were screened, and 231 full texts reviewed. 11 studies met inclusion criteria, but varied by age, race, year and proportion of participants who were C-peptide negative. Age at diagnosis was the most discriminatory feature in 7/9 studies where it was assessed, with optimal cut-offs (>70% mean sensitivity and specificity) across studies being <30 years or <40 years. Use of/time to insulin treatment and body mass index (BMI) were also discriminatory. When combining features, BMI added little over age at diagnosis and/or time to insulin (<1% improvement in classification). Conclusions Despite finding only 11 studies, and considerable heterogeneity between studies, age at diagnosis and time to insulin were consistently the most discriminatory criteria. BMI, despite being widely used in clinical practice, adds little to these two criteria. The criteria identified are similar to the Royal College of General Practitioners National Health Service (RCGP/NHS) Diabetes classification guidelines, which use age at diagnosis <35 years and time to insulin <6 m. Until further studies are carried out, these guidelines represent a suitable classification scheme. Systematic review registration PROSPERO reference CRD42012001736.

The impact of insulin administration during the mixed meal tolerance test.

Diabet. Med. 29, 1279–1284 (2012)

The impact of gender on urine C-peptide creatinine ratio interpretation

Background Urinary C-peptide creatinine ratio (UCPCR) is a non-invasive and convenient way of assessing endogenous insulin production. Adjusting for urine creatinine levels allows for differences in urine concentration. Creatinine excretion is known to be higher in men due to gender differences in muscle mass. We investigated the impact of gender on UCPCR. Methods One hundred and seventy-six subjects underwent a mixed meal tolerance test (MMTT). We looked at the relationship between UCPCR on urine C-peptide and creatinine excretion rates using timed post-meal urine samples. A further 415 subjects had two-hour post-meal UCPCR measurements in order to derive gender-specific percentiles for different diabetes subgroups and controls. Results UCPCR was 1.48-fold higher in women (n= 78) than men (n= 98), median (interquartile range [IQR]): 1.88 (0.49–3.49) men versus 2.88 (1.58–4.91) nmol mmol−1 women, P= 0.01. This reflects a gender difference in creatinine excretion rates (11.5 [8.3–13.7] men versus 8.2 [5.6–9.1] women μmol min−1 P < 0.001). C-peptide excretion rate was similar in men and women (19.8 [5.2–37.0] versus 22.1 [7.4–40.5] pmol min−1, P = 0.7). UCPCR was higher in women in all subgroups defined by diabetes classification and treatment, except long-term type 1 diabetes in whom C-peptide secretion was minimal. Conclusions Gender affects UCPCR, with higher values found in women. This results from lower urine creatinine reflecting gender differences in muscle mass. This necessitates gender-specific ranges for accurate interpretation of UCPCR results.