Mode of action of chloroquine in patients with non-insulin-dependent diabetes mellitus

Treating diabetes with combination of phosphodiesterase 5 inhibitors and hydroxychloroquine-a possible prevention strategy for COVID-19?

Type 2 diabetes (T2D) is one of the major risk factors for developing cardiovascular disease and the resultant devastating morbidity and mortality. The key features of T2D are hyperglycemia, hyperlipidemia, insulin resistance, and impaired insulin secretion. Patients with diabetes and myocardial infarction have worse prognosis than those without T2D. Moreover, obesity and T2D are recognized risk factors in developing severe form of COVID-19 with higher mortality rate. The current lines of drug therapy are insufficient to control T2D and its serious cardiovascular complications. Phosphodiesterase 5 (PDE5) is a cGMP specific enzyme, which is the target of erectile dysfunction drugs including sildenafil, vardenafil, and tadalafil. Cardioprotective effects of PDE5 inhibitors against ischemia/reperfusion (I/R) injury were reported in normal and diabetic animals. Hydroxychloroquine (HCQ) is a widely used antimalarial and anti-inflammatory drug and its hyperglycemia-controlling effect in diabetic patients is also under investigation. This review provides our perspective of a potential use of combination therapy of PDE5 inhibitor with HCQ to reduce cardiovascular risk factors and myocardial I/R injury in T2D. We previously observed that diabetic mice treated with tadalafil and HCQ had significantly reduced fasting blood glucose and lipid levels, increased plasma insulin and insulin-like growth factor-1 levels, and improved insulin sensitivity, along with smaller myocardial infarct size following I/R. The combination treatment activated Akt/mTOR cellular survival pathway, which was likely responsible for the salutary effects. Therefore, pretreatment with PDE5 inhibitor and HCQ may be a potentially useful therapy not only for controlling T2D but also reducing the rate and severity of COVID-19 infection in the vulnerable population of diabetics.

Diabetes-Modifying Antirheumatic Drugs: The Roles of DMARDs as Glucose-Lowering Agents

Systemic inflammation represents a shared pathophysiological mechanism which underlies the frequent clinical associations among chronic inflammatory rheumatic diseases (CIRDs), insulin resistance, type 2 diabetes (T2D), and chronic diabetes complications, including cardiovascular disease. Therefore, targeted anti-inflammatory therapies are attractive and highly desirable interventions to concomitantly reduce rheumatic disease activity and to improve glucose control in patients with CIRDs and comorbid T2D. Therapeutic approaches targeting inflammation may also play a role in the prevention of prediabetes and diabetes in patients with CIRDs, particularly in those with traditional risk factors and/or on high-dose corticosteroid therapy. Recently, several studies have shown that different disease-modifying antirheumatic drugs (DMARDs) used for the treatment of CIRDs exert antihyperglycemic properties by virtue of their anti-inflammatory, insulin-sensitizing, and/or insulinotropic effects. In this view, DMARDs are promising drug candidates that may potentially reduce rheumatic disease activity, ameliorate glucose control, and at the same time, prevent the development of diabetes-associated cardiovascular complications and metabolic dysfunctions. In light of their substantial antidiabetic actions, some DMARDs (such as hydroxychloroquine and anakinra) could be alternatively termed “diabetes-modifying antirheumatic drugs”, since they may be repurposed for co-treatment of rheumatic diseases and comorbid T2D. However, there is a need for future randomized controlled trials to confirm the beneficial metabolic and cardiovascular effects as well as the safety profile of distinct DMARDs in the long term. This narrative review aims to discuss the current knowledge about the mechanisms behind the antihyperglycemic properties exerted by a variety of DMARDs (including synthetic and biologic DMARDs) and the potential use of these agents as antidiabetic medications in clinical settings.

A review on the pharmacokinetic properties and toxicity considerations for chloroquine and hydroxychloroquine to potentially treat coronavirus patients

The SARS-CoV-2 virus, caused a novel emerged coronavirus disease, is growing rapidly worldwide. Few studies have evaluated the efficacy and safety of Chloroquine (CQ), an old antimalarial drug, and Hydroxychloroquine (HCQ) in the treatment of COVID-19 infection. HCQ is derived from CQ by adding a hydroxyl group into it and is a less toxic derivative of CQ for the treatment of COVID-19 infection because it is more soluble. This article summarizes pharmacokinetic properties and toxicity considerations for CQ and HCQ, drug interactions, and their potential efficacy against COVID-19. The authors also look at the biochemistry changes and clinical uses of CQ and HCQ, and supportive treatments following toxicity occurs. It was believed that CQ and HCQ may provide few benefits to COVID-19 patients. A number of factors should be considered to keep the drug safe, such as dose, in vivo animal toxicological findings, and gathering of metabolites in plasma and/or tissues. The main conclusion of this review is that CQ and HCQ with considered to their ADMET properties has major shortcomings and fully irresponsible.

Possible mechanisms of the hypoglycaemic effect of artesunate: Gender implication

Background

We investigated the mechanism of artesunate’s glucose-modulating effect especially with gender implication.

Methods

Twenty-five (25) male and 25 female rats were separately and blindly allocated into five identical groups (n = 5/group). Group I (control) received 0.2 ml/kg distilled water. Groups II and III both received 2.90 mg/kg artesunate on day one, but 1.45 mg/kg from day two till day five and day fifteen respectively. Groups IV and V both received 8.70 mg/kg artesunate on day one, but 4.35 mg/kg artesunate from day two till day five and day fifteen respectively.

Results

In male rats, glucose was reduced by both doses of artesunate at 5 days but increased by high dose at 15 days. Artesunate increased glycogen concentration at short duration which normalised at long duration in both genders. Artesunate increased G6P concentration only in male rats at 15 days but reduced G6Pase activity in male and female rats (except in those that received low and high doses of artesunate for 15 days). Artesunate increased insulin only in male rats treated with low dose artesunate for 5 days. Artesunate increased cortisol concentration in male but reduced it in female rats. Artesunate decreased glucagon concentration except in female rats treated with high dose for 5 days. Artesunate increased oestrogen concentration in male rats that received low dose artesunate for 5 days but reduced it in female rats that received high dose for 15 days.

Conclusions

Artesunate reduces plasma glucose by reducing plasma glucagon concentrations and inhibiting liver glycogenolysis via inhibition of G6Pase activity in both sexes. Increase in insulin concentration contributed to the reduction in blood glucose caused by artesunate in male but not female rats; and artesunate-induced increase in G6P, a substrate for G6PD, could enhance NADPH generation and antioxidant enzyme activation in male rats.

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Reducing glucagon concentration and inhibiting G6Pase activity in both genders. .

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Increasing plasma insulin in male but not in female.

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Increasing G6P, a substrate for G6PD, in male rats.

Repurposing New Use for Old Drug Chloroquine against Metabolic Syndrome: A Review on Animal and Human Evidence

Chloroquine (CQ) and hydroxychloroquine (HCQ) are traditional anti-malarial drugs that have been repurposed for new therapeutic uses in many diseases due to their simple usage and cost-effectiveness. The pleiotropic effects of CQ and HCQ in regulating blood pressure, glucose homeostasis, lipid, and carbohydrate metabolism have been previously described in vivo and in humans, thus suggesting their role in metabolic syndrome (MetS) prevention. The anti-hyperglycaemic, anti-hyperlipidaemic, cardioprotective, anti-hypertensive, and anti-obesity effects of CQ and HCQ might be elicited through reduction of inflammatory response and oxidative stress, improvement of endothelial function, activation of insulin signalling pathway, inhibition of lipogenesis and autophagy, as well as regulation of adipokines and apoptosis. In conclusion, the current state of knowledge supported the repurposing of CQ and HCQ usage in the management of MetS.

Molecular Insights into the MAPK Cascade during Viral Infection: Potential Crosstalk between HCQ and HCQ Analogues

The mitogen-activated protein kinase (MAPK) pathway links the cell-surface receptors to the transcription machinery, transducing the extracellular signals into several outputs, which may also adapt the host defense mechanism to viral attacks. The Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2) that causes the COrona VIrus Disease 2019 (COVID-19) has infected upwards of nearly 70 million people and worldwide has claimed more than 1,600,000 deaths. So far, there continues to be no specific treatment for this novel coronavirus-induced disease. In the search to control the global COVID-19 pandemic, some eastern and developing countries have approved a variety of treatments with controversial efficacy, among which is the use of the antimalarial hydroxychloroquine (HCQ). Interestingly, prior data had indicated that the HCQ/CQ could influence the MAPK cascade. The main aim of this review is to address molecular mechanisms, beyond drugs, that can be helpful against viral infection for this and future pandemics. We will highlight (1) the contribution of the MAPK cascade in viral infection and (2) the possible use of MAPK inhibitors in curbing viral infections, alone or in combination with HCQ and quinoline analogues. We are convinced that understanding the molecular patterns of viral infections will be critical for new therapeutical approaches to control this and other severe diseases.

An umbrella review of systematic reviews with meta-analyses evaluating positive and negative outcomes of Hydroxychloroquine and chloroquine therapy

BACKGROUND & AIMS

Hydroxychloroquine (HCQ) and chloroquine (CQ) are anti-malarial drugs frequently used in the rheumatologic field. They were recently identified as potential therapeutic options for Coronavirus Disease (COVID-19). The present study aims to map and grade the diverse health outcomes associated with HCQ/CQ using an umbrella review approach.

METHODS

Umbrella review of systematic reviews of observational and intervention studies. For observational studies, random-effects summary effect size, 95% confidence interval, and 95% prediction interval were estimated. We also assessed heterogeneity, evidence for small-study effect, and evidence for excess significance bias. The quality of evidence was then graded using validated criteria from highly convincing to weak. The evidence from randomized controlled trials (RCTs) was graded using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) tool.

RESULTS

From 313 articles returned in the literature search, six meta-analyses were included (n = 25 outcomes). Among meta-analyses (MAs) of observational studies, HCQ/CQ are weakly associated with a reduced risk for cardiovascular events and diabetes when used for autoimmune diseases and with spontaneous abortion; they are also associated with a higher risk of death in COVID-19 patients. Among MAs of RCTs, HCQ/CQ are associated with an improvement of articular manifestations of rheumatic diseases.

CONCLUSIONS

There is high evidence of the efficacy of HCQ/CQ in the rheumatologic field. The lack of evidence for efficacy and the risk of death associated with the use of HCQ/CQ for COVID-19 indicate the inappropriateness of their inclusion in recent COVID-19 therapy guidelines and the urgent need for RCTs to determine eventual appropriateness as a COVID-19 therapy.

Dissecting the interaction between COVID-19 and diabetes mellitus

Coronavirus disease 2019 (COVID-19) is a global pandemic that is caused by a novel coronavirus, severe acute respiratory syndrome coronavirus-2. Data from several countries have shown higher morbidity and mortality among individuals with chronic metabolic diseases, such as diabetes mellitus. In this review, we explore the contributing factors for poorer prognosis in these individuals. As a significant proportion of patients with COVID-19 also have diabetes mellitus, this adds another layer of complexity to their management. We explore potential interactions between antidiabetic medications and renin-angiotensin-aldosterone system inhibitors with COVID-19. Suggested recommendations for the use of antidiabetic medications for COVID-19 patients with diabetes mellitus are provided. We also review pertinent clinical considerations in the management of diabetic ketoacidosis in COVID-19 patients. In addition, we aim to increase clinicians' awareness of the metabolic effects of promising drug therapies for COVID-19. Finally, we highlight the importance of timely vaccinations for patients with diabetes mellitus.

COVID-19 prevention and treatment: A critical analysis of chloroquine and hydroxychloroquine clinical pharmacology

Nicholas White and coauthors discuss chloroquine and hydroxychloroquine pharmacology in the context of possible treatment of SARS-CoV-2 infection.

Risk of Incident Diabetes Mellitus Associated With the Dosage and Duration of Oral Glucocorticoid Therapy in Patients With Rheumatoid Arthritis

Objective

To quantify the risk of incident diabetes mellitus (DM) associated with the dosage, duration, and timing of glucocorticoid (GC) use in patients with rheumatoid arthritis (RA).

Methods

We undertook a cohort study using 2 databases: a UK primary care database (the Clinical Practice Research Datalink [CPRD]) including 21,962 RA patients (1992–2009) and the US National Data Bank for Rheumatic Diseases (NDB) including 12,657 RA patients (1998–2013). Information on the dosage and timing of GC use was extracted. DM in the CPRD was defined using Read codes, at least 2 prescriptions for oral antidiabetic medication, or abnormal blood test results. DM in the NDB was defined through patient self‐reports. Data were analyzed using time‐dependent Cox models and a novel weighted cumulative dose (WCD) model that accounts for dosage, duration, and timing of treatment.

Results

The hazard ratio (HR) was 1.30 (95% confidence interval [95% CI] 1.17–1.45) and 1.61 (95% CI 1.37–1.89) in current GC users compared to nonusers in the CPRD and the NDB, respectively. A range of conventional statistical models consistently confirmed increases in risk with the GC dosage and duration. The WCD model showed that recent GC use contributed the most to the current risk of DM, while doses taken >6 months previously did not influence current risk. In the CPRD, 5 mg of prednisolone equivalent dose for the last 1, 3, and 6 months was significantly associated with HRs of 1.20, 1.43, and 1.48, respectively, compared to nonusers.

Conclusion

GC use is a clinically important and quantifiable risk factor for DM. Risk is influenced by the dosage and treatment duration, although only for GC use within the last 6 months.

Chloroquine increases phosphorylation of AMPK and Akt in myotubes

Aims

There are reports that ataxia telangiectasia mutated (ATM) can activate the AMP-activated protein kinase (AMPK) and also Akt, two kinases that play integral parts in cardioprotection and metabolic function. We hypothesized that chloroquine and resveratrol, both known ATM activators, would also activate AMPK and Akt.

Main methods

Phosphorylation of AMPK and Akt was assessed after C2C12 myotubes were exposed to chloroquine or resveratrol. Additional experiments were done in cells expressing shRNA against ATM or in the presence of the ATM inhibitor KU55933. The effects of chloroquine on intracellular calcium were assessed with the fluorescent probe Calcium Green-1 AM.

Key findings

0.5 mM chloroquine increased AMPK phosphorylation by nearly four-fold (P < 0.05), and 0.25 mM chloroquine roughly doubled Akt phosphorylation (P < 0.05). Chloroquine also increased autophosphorylation of ATM by ∼50% (P < 0.05). Resveratrol (0.15 mM) increased AMPK phosphorylation about three-fold (P < 0.05) but in contrast to chloroquine sharply decreased Akt phosphorylation. Chloroquine increased AMPK and Akt phosphorylation in myotubes expressing shRNA against ATM that reduced ATM protein levels by about 90%. Likewise, chloroquine-stimulated phosphorylation of AMPK and Akt and resveratrol-stimulated phosphorylation of AMPK were not altered by inhibition of ATM. Chloroquine decreased intracellular calcium by >50% concomitant with a decrease in glucose transport.

Significance

These ATM-independent effects of chloroquine on AMPK and Akt and the additional effect to decrease intracellular calcium are likely to partially underlie the positive metabolic effects of chloroquine that have been reported in the literature.

Autophagy in adipose tissue and the beta cell: implications for obesity and diabetes

Autophagy is a lysosomal degradation pathway recycling intracellular long-lived proteins and damaged organelles, thereby maintaining cellular homeostasis. In addition to inflammatory processes, autophagy has been implicated in the regulation of adipose tissue and beta cell functions. In obesity and type 2 diabetes autophagic activity is modulated in a tissue-dependent manner. In this review we discuss the regulation of autophagy in adipose tissue and beta cells, exemplifying tissue-specific dysregulation of autophagy and its implications for the pathophysiology of obesity and type 2 diabetes. We will highlight common themes and outstanding gaps in our understanding, which need to be addressed before autophagy could be envisioned as a therapeutic target for the treatment of obesity and diabetes.

A favorable effect of hydroxychloroquine on glucose and lipid metabolism beyond its anti-inflammatory role

Hydroxychloroquine (HCQ), a commonly used antimalarial drug in rheumatic diseases, has shown favorable metabolic effects on both glucose control and lipid profiles. We describe a case of a young woman with type 1 diabetes whose glycemic control was optimized with the introduction of HCQ as a treatment for her Sjogren syndrome in addition to a subtle yet measurable improvement in her lipid profile. An increasing body of evidence supports the beneficial impacts of HCQ in various ancillary conditions, including diabetes mellitus and dyslipidemia. However, mechanisms of action responsible for these effects remain ill-defined and may include alterations in insulin metabolism and signaling through cellular receptors. These favorable metabolic effects of HCQ and further understanding of underlying mechanisms may provide an additional rational for its use in rheumatic diseases, conditions associated with an elevated cardiovascular risk.

Obesity activates a program of lysosomal-dependent lipid metabolism in adipose tissue macrophages independently of classic activation

Obesity activates a complex systemic immune response that includes the recruitment of macrophages and other immune cells to key metabolic tissues. Current models postulate that obesity and excess lipids classically activate macrophages, polarizing them toward an M1 (inflammatory) state. Little is known about noninflammatory functions of adipose tissue macrophages (ATMs). Here, we show that the expansion of adipose tissue (AT) across models of obesity induces a program of lysosome biogenesis in ATMs and is associated with lipid catabolism but not a classic inflammatory phenotype. This program is induced by factors produced by AT and is tightly coupled to lipid accumulation by ATMs. Inhibition of ATM lysosome function impairs lipid metabolism and increases lipid content in ATMs and reduces whole AT lipolysis. These data argue that ATMs contribute quantitatively to the development of obesity-induced inflammation but also serve an important role in lipid trafficking independent of their inflammatory phenotype.

Hydroxychloroquine: from malaria to autoimmunity

Quinine was first recognized as a potent antimalarial agent hundreds of years ago. Since then, the beneficial effects of quinine and its more advanced synthetic forms, chloroquine and hydroxychloroquine, have been increasingly recognized in a myriad of other diseases in addition to malaria. In recent years, antimalarials were shown to have various immunomodulatory effects, and currently have an established role in the management of rheumatic diseases, such as systemic lupus erythematosus and rheumatoid arthritis, skin diseases, and in the treatment of chronic Q fever. Lately, additional metabolic, cardiovascular, antithrombotic, and antineoplastic effects of antimalarials were shown. In this review, we discuss the known various immunomodulatory mechanisms of antimalarials and the current evidence for their beneficial effects in various diseases and in potential novel applications.

Changes in glycosylated hemoglobin after initiation of hydroxychloroquine or methotrexate treatment in diabetes patients with rheumatic diseases

OBJECTIVE

Prior research demonstrates that hydroxychloroquine (HCQ) lowers glycosylated hemoglobin (HbA(1c) ) in diabetes patients without rheumatic disease. We examined medical records of patients with diabetes mellitus (DM) and concomitant rheumatic illness to measure changes in HbA(1c) after starting HCQ or methotrexate (MTX).

METHODS

We used electronic medical records to identify patients beginning treatment with either HCQ or MTX who had a diagnosis of DM (or a pretreatment HbA(1c) value of ≥7%) and at least 1 HbA(1c) measurement both before and within 12 months after initiation of treatment. Using a structured medical record abstraction, we examined rheumatic disease diagnosis, cumulative steroid use, duration (months) between drug initiation and lowest HbA(1c) value, a change in DM medication, body mass index (BMI), age, and sex. Adjusted linear regression models determined changes in HbA(1c) from pretreatment values to the lowest posttreatment values within 12 months.

RESULTS

We identified 45 patients taking HCQ and 37 patients taking MTX who met the inclusion criteria. Rheumatoid arthritis had been diagnosed in approximately half of the patients in each group. Age, sex, and mean pretreatment HbA(1c) levels were similar across groups. The mean BMI of those taking HCQ (35.4 kg/m(2) ) was slightly higher than that of those taking MTX (32.2 kg/m(2) ) (P = 0.13). Glucocorticoid use appeared more common in those taking MTX (46%) than in those taking HCQ (29%) (P = 0.17). The mean reduction in HbA(1c) from pretreatment values to the lowest posttreatment values was 0.66% (95% confidence interval [95% CI] 0.26, 1.05) in those taking HCQ compared with 0.11% (95% CI -0.18, 0.40) in those taking MTX. In fully adjusted analyses, the reduction in HbA(1c) among those taking HCQ was 0.54% greater than the reduction among those taking MTX (P = 0.041).

CONCLUSION

HCQ initiation was associated with a significantly greater reduction in HbA(1c) as compared with MTX initiation among diabetes patients with rheumatic disease.

Hydroxychloroquine and glycemia in women with rheumatoid arthritis and systemic lupus erythematosus

OBJECTIVE

To determine the relationship between current hydroxychloroquine (HCQ) use and 2 indicators of glycemic control, fasting glucose and insulin sensitivity, in nondiabetic women with systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA).

METHODS

Nondiabetic women with SLE (n = 149) or RA (n = 177) recruited between 2000 and 2005 for a cross-sectional evaluation of cardiovascular risk factors were characterized by HCQ usage status. Unadjusted and multivariately adjusted mean fasting glucose, median insulin, and insulin resistance [assessed by the homeostasis model assessment (HOMA-IR) calculation] were compared among HCQ users and nonusers for disease-specific groups.

RESULTS

More women with SLE were taking HCQ than those with RA (48% vs 18%; p < 0.0001; mean dose ~ 400 mg vs ~ 200 mg). For women with SLE or RA, after adjustment for age, waist circumference, disease duration, prednisone dosage, C-reactive protein, menopausal status, nonsteroidal antiinflammatory drugs, and disease-specific indicators, serum glucose was lower in HCQ users than in nonusers (SLE: 85.9 vs 89.3 mg/dl, p = 0.04; RA: 82.5 vs 86.6 mg/dl, p = 0.05). In women with SLE, HCQ use also was associated with lower (log)HOMA-IR (0.97 vs 1.12, p = 0.09); in those with RA, no differences in (log)HOMA-IR were seen. HCQ usage was not associated with fasting insulin levels in either patient group.

CONCLUSION

HCQ use was associated with lower fasting glucose in women with SLE or RA and also lower (log)HOMA-IR in the SLE group. The use of HCQ may be beneficial for reducing cardiovascular risk by improving glycemic control in these patients.

Hydroxychloroquine: a diabetic drug in disguise?

Hydroxychloroquine (HCQ) is an antimalarial agent that is commonly used to treat rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). The present report documents a case of hypoglycaemia due to HCQ in a patient with SLE and diabetes mellitus type 2, in which the HCQ completely replaced the need for daily subcutaneous insulin.

Inverse relationship between peripheral insulin removal and action: studies with metformin

The interaction of insulin with metformin on muscle glucose metabolism was examined in the perfused rat hindquarter. Glucose, lactate, and insulin were measured at the inflow to and outflow from the hindquarter, which was perfused with human erythrocytes suspended in a Kreb's-Ringer albumin buffer for 120 min. Perfusions were performed with no additions (I) and with insulin infusions targeted to concentrations of 175 (II) and 350 pmol/l (III) as well as infusions targeted to levels of 0 (IV), 70 (V), and 175 pmol/l (VI) but in the presence of metformin (90 microg/ml). In the presence of metformin, identical infusion rates of insulin yielded higher insulin concentrations, namely 283 +/- 19 vs. 202 +/- 31 pmol/l for VI and II, respectively (P < 0.05). Glucose uptake (GU) increased correspondingly to 79.8 +/- 0.8 in VI from 60.8 +/- 2.1 for IV and 50.1 +/- 1.3 for II and 46.1 +/- 2.7 mg/120 min for I (P < 0.05). This enhanced GU was matched by increasing insulin levels using only a higher rate of its infusion (III): GU of 70.2 +/- 2.4 mg/120 min with insulin of 334 +/- 26 pmol/l (P > 0.05). The simple concurrent presence of metformin and insulin [matching insulin concentrations in II rather than infusion rates (IV)] demonstrated no additonal effect on GU above that of metformin. The synergistic effects of metformin and insulin could thus be explained by a metformin-mediated decrease in the extraction of insulin by the hindquarter (4.8 +/- 0.4% vs. 8.6 +/- 0.9%, P < 0.05). This increases interstitial insulin (and, in a closed system, perfusate insulin), which acts on cell surface receptors to increase glucose uptake. The results demonstrate that the extracellular insulin concentration, rather than insulin internalization and degradation, is the primary determinant of insulin action on GU in muscle and that changes in tissue insulin extraction may alter local concentrations and, therefore, systemic insulin sensitivity. This provides both a physiological mechanism and a possible therapeutic target for improving insulin sensitivity.

Chloroquine augments the binding of insulin to its receptor

The effect of chloroquine on the interaction of insulin with its receptor has been investigated under both equilibrium and non-equilibrium conditions. Chloroquine was found to augment insulin binding in a pH-dependent manner between pH 6.0 and pH 8.5, with the maximum occurring at approximately pH 7.0. Analysis of the equilibrium binding data in terms of independent binding sites gave equivocal results but suggested an increase in the high-affinity component. Analysis using the negative co-operativity binding model of De Meyts, Bianco and Roth [J. Biol. Chem. (1976) 251, 1877-1888] suggested that the affinity at both high and low occupancy was increased equally. The kinetics of association of insulin with the plasma-membrane receptor indicated that, although the net rate of association increased in the presence of chloroquine, this was due to a reduction in the dissociation rate rather than an increase in the association rate. This was confirmed by direct measurement of the rates of dissociation. Dissociation was found to be distinctly biphasic, with fast and slow components. Curve fitting suggested that the decrease in dissociation rate in the presence of chloroquine was not due to a decrease in either of the two dissociation rate constants, but rather to an increase in the amount of insulin dissociating by the slow component. It was also found that the increase in dissociation rate in the presence of excess insulin, ascribed to negative co-operativity, could be accounted for by an increase in the amount of insulin dissociating by the faster pathway, rather than by an increase in the dissociation rate constant. Thus chloroquine appears to have the opposite effect to excess insulin, and evidence was found for the induction of positive co-operativity in the insulin-receptor interaction at high chloroquine concentrations. Evidence was also found for the presence of low-affinity chloroquine binding sites with binding parameters similar to the concentration dependence of the chloroquine-induced augmentation of insulin binding.