Insulin resistance limits corneal nerve regeneration in patients with type 2 diabetes undergoing intensive glycemic control

Differential Effects of Visceral and Subcutaneous Adiposity on Peripheral Neuropathy

OBJECTIVE

Obesity increases the risk of diabetic neuropathy. This study investigates the impact of visceral (VAT) and subcutaneous adipose tissue (SAT) volume on peripheral neuropathy.

METHODS

A total of 302 adults from the Qatar Biobank (QBB) underwent iDXA to measure VAT and SAT volumes, intima media thickness (IMT), and peripheral neuropathy assessments using corneal confocal microscopy (CCM), vibration perception threshold (VPT), and the DN4 questionnaire.

RESULTS

The QBB cohort was aged 43.9 ± 12.9 years, of whom 43.7% were women, 42.1% had obesity, 17.4% had type 2 diabetes (T2D) and 10.9% had hypertension. VAT was associated with T2D, hypertension, higher HbA1c, diastolic blood pressure, triglycerides, and inflammatory markers, and lower HDL (p < 0.0001). There were no significant associations between SAT and these cardiovascular risk factors. VAT volume was associated with lower corneal nerve inferior whorl length (IWL) (p < 0.05) and higher VPT (p = 0.01), partially mediated by elevated HbA1c (p < 0.05, p = 0.001) and IMT (p < 0.0001), while its association with neuropathic symptoms was fully mediated by systolic blood pressure (p < 0.05), T2D (p < 0.01), and triglycerides (p = 0.05). SAT showed no associations with measures of neuropathy.

CONCLUSIONS

VAT but not SAT is associated with peripheral neuropathy. This study underscores the need to target VAT to improve neuropathy.

Enhancing Corneal Sensitivity in Diabetic Patients Through an Innovative Ophthalmic Solution: In Vivo and Vitro Results

Background/Objectives: Diabetes is a well-recognised factor inducing a plethora of corneal alterations ranging from dry eye to reduced corneal sensibility, epithelial defects, and reduced cicatrisation. This cohort study aimed to assess the efficacy of a novel ophthalmic solution combining cross-linked hyaluronic acid (CHA), chondroitin sulfate (CS), and inositol (INS) in managing diabetes-induced corneal alterations. Specifically, it evaluated the solution's impact on the tear breakup time (TBUT), the ocular surface disease index (OSDI), and corneal sensitivity after three months of treatment. Additionally, the solution's potential to promote wound healing was examined. Methods: Two different populations were retrieved from the database; the first one was composed of 20 diabetic subjects treated for three months with the ophthalmic CAH-CS (OPHTAGON srl, Rome, Italy), while the second group was composed of 20 diabetic subjects who did not want to use any eye lubricant or other treatment. The outcome measures were the TBUT, the OSDI score, and the corneal sensitivity measured using a Cochet-Bonnet aesthesiometer. To investigate the wound-healing properties, in vitro tests were conducted using two cell lines, comparing the results of scratch tests with and without the solution. Results: The results indicate that CHA-CS significantly improved the tear film stability, as evidenced by an increased TBUT and a reduction in dry eye symptoms reflected by lower OSDI scores. Moreover, the solution was associated with an enhanced corneal sensitivity in treated patients. In wound-healing assays, CHA-CS promoted cell motility, suggesting a supportive role in tissue repair compared to untreated cells. Conclusions: Collectively, the results suggest that CHA-CS could serve as an innovative tool for the treatment of diabetic patients with corneal alterations and delayed corneal sensitivity. Clinical trial registration number: Clinical Trial.gov NCT06573606.

Glucose-lowering medication associated with weight loss may limit the progression of diabetic neuropathy in type 2 diabetes

AIM

Obesity is a major risk factor for diabetic peripheral neuropathy (DPN) in type 2 diabetes (T2D). This study investigated the effect of glucose lowering medication associated with weight change on DPN.

METHODS

Participants with T2D were grouped based on whether their glucose lowering medications were associated with weight gain (WG) or weight loss (WL). They underwent clinical, metabolic testing and assessment of neuropathic symptoms, vibration perception threshold (VPT), sudomotor function and corneal confocal microscopy (CCM) at baseline and follow-up between 4 and 7 years.

RESULTS

Of 76 participants, 69.7% were on glucose lowering medication associated with WG, and 30.3% were on glucose lowering medication associated with WL. At baseline, participants in the WG group had a significantly longer duration of diabetes (p < .01), higher douleur neuropathique en 4 (DN4) score (p < .0001) and VPT (p = .01) compared with those in the WL group. Over a 56-month period, participants in the WG group showed no significant change in body weight (p = .11), HbA1c (p = .18), triglycerides (p = .42), DN4 (p = .11), VPT (p = .15) or Sudoscan (p = .43), but showed a decline in corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD) and corneal nerve fiber length (CNFL) (p < .0001). Participants in the WL group showed a reduction in weight (p = .01) and triglycerides (p < .05), no change in DN4 (p = .30), VPT (p = .31) or Sudoscan (p = .17) and a decline in the corneal nerve branch density (p < .01).

CONCLUSIONS

Participants treated with glucose lowering medication associated with weight gain had worse neuropathy and greater loss of corneal nerves during follow-up, compared to patients treated with medication associated with weight loss.

Corneal nerve loss in adolescents with obesity and acanthosis nigricans

BACKGROUND/AIM

Obesity and related metabolic abnormalities in adults are associated with peripheral neuropathy. Acanthosis nigricans (AN) is associated with insulin resistance, fatty liver, hyperlipidemia and glucose intolerance, all of which are risk factors for neuropathy. The aim of this study was to investigate if obese adolescents with AN have evidence of small nerve fiber damage.

MATERIAL AND METHODS

Adolescents with obesity with and without AN underwent body composition analysis, assessment of vibration perception threshold (VPT), monofilament sensitivity and corneal confocal microscopy (CCM) to quantify corneal nerve fiber density (CNFD), branch density (CNBD), length (CNFL) and inferior whorl length (IWL).

RESULTS

Forty-six participants with obesity with (n = 31) and without (n = 15) AN aged 15(14-17) years were compared to 20 healthy controls aged 13(12-14) years. There was no difference in VPT, monofilament sensitivity and CCM measures between adolescents with obesity and controls. However, adolescents with AN had a significantly higher weight (P = 0.022), fat% (P = 0.029) and fat-muscle ratio (P = 0.012) with a lower CNFD (P = 0.045) compared to those with obesity without AN.

CONCLUSION

Adolescents with obesity and acanthosis nigricans have a higher fat mass and small nerve fibre loss, indicative of a sub-clinical neuropathy.

The Role of Insulin-like Growth Factor (IGF) System in the Corneal Epithelium Homeostasis-From Limbal Epithelial Stem Cells to Therapeutic Applications

The corneal epithelium, comprising three layers of cells, represents the outermost portion of the eye and functions as a vital protective barrier while concurrently serving as a critical refractive structure. Maintaining its homeostasis involves a complex regenerative process facilitated by the functions of the lacrimal gland, tear film, and corneal nerves. Crucially, limbal epithelial stem cells located in the limbus (transitional zone between the cornea and the conjunctiva) are instrumental for the corneal epithelium integrity by replenishing and renewing cells. Re-epithelialization failure results in persistent defects, often associated with various ocular conditions including diabetic keratopathy. The insulin-like growth factor (IGF) system is a sophisticated network of insulin and other proteins essential for numerous physiological processes. This review examines its role in maintaining the corneal epithelium homeostasis, with a special focus on the interplay with corneal limbal stem cells and the potential therapeutic applications of the system components.

Prevalence and risk factors for diabetic peripheral neuropathy, neuropathic pain and foot ulceration in the Arabian Gulf Region

Aims/Introduction

This study determined the prevalence and risk factors for diabetic peripheral neuropathy (DPN), painful DPN and diabetic foot ulceration (DFU) in patients with type 2 diabetes in secondary healthcare in Qatar, Kuwait and the Kingdom of Saudi Arabia.

Materials and Methods

Adults aged 18–85 years with type 2 diabetes were randomly enrolled from secondary healthcare, and underwent clinical and metabolic assessment. DPN was evaluated using vibration perception threshold and neuropathic symptoms and painful Diabetic Peripheral Neuropathy was evaluated using the Douleur Neuropathique 4 questionnaire.

Results

A total of 3,021 individuals were recruited between June 2017 and May 2019. The prevalence of DPN was 33.3%, of whom 52.2% were at risk of DFU and 53.6% were undiagnosed. The prevalence of painful DPN was 43.3%, of whom 54.3% were undiagnosed. DFU was present in 2.9%. The adjusted odds ratios for DPN and painful DPN were higher with increasing diabetes duration, obesity, poor glycemic control and hyperlipidemia, and lower with greater physical activity. The adjusted odds ratio for DFU was higher with the presence of DPN, severe loss of vibration perception, hypertension and vitamin D deficiency.

Conclusions

This is the largest study to date from the Middle East showing a high prevalence of undiagnosed DPN, painful DPN and those at risk of DFU in patients with type 2 diabetes, and identifies their respective risk factors.

Corneal Confocal Microscopy to Image Small Nerve Fiber Degeneration: Ophthalmology Meets Neurology

Neuropathic pain has multiple etiologies, but a major feature is small fiber dysfunction or damage. Corneal confocal microscopy (CCM) is a rapid non-invasive ophthalmic imaging technique that can image small nerve fibers in the cornea and has been utilized to show small nerve fiber loss in patients with diabetic and other neuropathies. CCM has comparable diagnostic utility to intraepidermal nerve fiber density for diabetic neuropathy, fibromyalgia and amyloid neuropathy and predicts the development of diabetic neuropathy. Moreover, in clinical intervention trials of patients with diabetic and sarcoid neuropathy, corneal nerve regeneration occurs early and precedes an improvement in symptoms and neurophysiology. Corneal nerve fiber loss also occurs and is associated with disease progression in multiple sclerosis, Parkinson's disease and dementia. We conclude that corneal confocal microscopy has good diagnostic and prognostic capability and fulfills the FDA criteria as a surrogate end point for clinical trials in peripheral and central neurodegenerative diseases.

Diabetic Corneal Neuropathy: Pathogenic Mechanisms and Therapeutic Strategies

Diabetes mellitus (DM) is a major global public health problem that can cause complications such as diabetic retinopathy, diabetic neuropathy, and diabetic nephropathy. Besides the reporting of reduction in corneal nerve density and decrease in corneal sensitivity in diabetic patients, there may be a subsequent result in delayed corneal wound healing and increased corneal infections. Despite being a potential cause of blindness, these corneal nerve changes have not gained enough attention. It has been proposed that corneal nerve changes may be an indicator for diabetic neuropathy, which can provide a window for early diagnosis and treatment. In this review, the authors aimed to give an overview of the relationship between corneal nerves and diabetic neuropathy as well as the underlying pathophysiological mechanisms of corneal nerve fiber changes caused by DM for improved prediction and prevention of diabetic neuropathy. In addition, the authors summarized current and novel therapeutic methods for delayed corneal wound healing, nerve protection and regeneration in the diabetic cornea.