Telehealth uptake among middle-aged and older Americans during COVID-19: chronic conditions, social media communication, and race/ethnicity

OBJECTIVES

This study investigated whether and to what extent constructs of the protection motivation theory of health (PMT)-threat appraisal (perceived vulnerability/severity) and coping appraisal (response efficacy and self-efficacy)-are related to telehealth engagement during the COVID-19 pandemic, and how these associations differ by race/ethnicity among middle-aged and older Americans.

METHODS

Data were from the 2020 Health and Retirement Study. Multivariable ordinary least-squares regression analyses were computed adjusting for health and sociodemographic factors.

RESULTS

Some PMT constructs are useful in understanding telehealth uptake. Perceived vulnerability/severity, particularly comorbidity (b = 0.13, 95% confidence interval (CI) [0.11, 0.15], p < 0.001), and response efficacy, particularly participation in communication via social media (b = 0.24, 95% CI [0.21, 0.27], p < 0.001), were significantly and positively associated with higher telehealth uptake during the COVID-19 pandemic among middle-aged and older Americans. Non-Hispanic Black adults were more likely to engage in telehealth during the pandemic than their non-Hispanic White counterparts (b = 0.20, 95% CI [0.12, 0.28], p < 0.001). Multiple moderation analyses revealed the significant association between comorbidity and telehealth uptake was similar across racial/ethnic groups, whereas the significant association between social media communication and telehealth uptake varied by race/ethnicity. Specifically, the association was significantly less pronounced for Hispanic adults (b = -0.11, 95% CI [-0.19, -0.04], p < 0.01) and non-Hispanic Asian/other races adults (b = -0.13, 95% CI [-0.26, -0.01], p < 0.05) than it was for their non-Hispanic White counterparts.

CONCLUSION

Results suggest the potential of using social media and telehealth to narrow health disparities, particularly serving as a bridge for members of underserved communities to telehealth uptake.

Communication Modalities, Personality Traits, and Change in Perceived Control Over Social Life Following Onset of the COVID-19 Pandemic Among Older Americans

We examined associations between change in social contact communication modalities and change in perceived control over social life (PCOSL) following onset of the COVID-19 pandemic among older Americans and evaluated the extent to which associations were moderated by personality. Data were from the 2016 and 2020 waves of the Health and Retirement Study. Multivariate ordinary least squares regression analyses were computed adjusting for baseline PCOSL, sociodemographic, health, and psychosocial factors. Multiple moderation analyses revealed that extraversion moderated the association between change in social media communication and change in PCOSL before to during COVID-19. As levels of engagement in social media communication increased, those with high extraversion experienced increases in PCOSL, whereas those with low extraversion experienced decreases in PCOSL. Findings suggest that social interventions targeting perceived control and communication modality may be useful for older adults during global health events and that personality characteristics can help to inform intervention choices.

Aging alone and financial insecurity predict depression: a path analysis of objective and subjective indices

OBJECTIVES

This study draws on conservation of resources theory and transactional stress theory to guide our understanding of how social isolation, financial insecurity, and social support serve as a balance of both risk and protection for late-life depression.

METHODS

Data were from the Leave-Behind Questionnaire in the 2016 (N = 4293) and 2018 (N = 4714) waves of the Health and Retirement Study. We conducted a cross-sectional path analysis via structural equation modeling, including objective and subjective perspectives. The same model was tested in both samples.

RESULTS

Both social isolation and financial insecurity were associated with depression. We found several mediating risks and protective factors of these relationships. Objective financial status affected depression through both perceived financial insecurity and perceived social isolation, whereas objective isolation affected depression through perceived social support. This mediation model was -significant after adjusting for confounders.

CONCLUSION

This study underscores the importance of investigating the balance between risk and protection for depression, in the rising number of older adults aging alone in society. Findings suggest that objective and perceived measures offer unique windows into psychological constructs. Considering both objective and subjective perspectives may provide alternative targets for subsequent interventions to improve mental health in later life.

Telehealth Use Among Older Adults With Sensory, Cognitive, and Physical Impairments: A Substitute or Supplement to Traditional Care?

OBJECTIVES

Telehealth use flourished during the COVID-19 pandemic, as older patients faced obstacles to seeking in-person care. Heavy reliance on telehealth may continue postpandemic, due to increased Medicare investments in its use. However, it is unclear if older adults with disabilities face obstacles to effective telehealth use. We evaluate (a) how sensory, physical, and cognitive impairments affect older adults' use of telehealth only, traditional in-person care only, neither, or both (i.e., combined care); and (b) whether these patterns differ on the basis of socioeconomic and social resources that may facilitate telehealth use.

METHOD

Data are from the Self-Administered Questionnaire in the 2020 wave of the Health and Retirement Study (n = 4,453). We estimated multinomial logistic regression models to evaluate associations between impairments and health care service use and tested 2-way interaction terms to evaluate moderation effects.

RESULTS

Persons without impairments were most likely to use combined care, considered the optimal form of care. Persons with vision or cognitive impairment were more likely to use telehealth or traditional care only, whereas persons with 3 or more physical limitations were least likely to use telehealth alone, relative to combined care. Patterns did not differ significantly on the basis of any of the potential moderators.

DISCUSSION

We discuss implications for health care policy and practice, in light of reimbursement changes proposed by the Centers for Medicare and Medicaid Services for telehealth services. These proposals include the elimination of voice-only services which may be particularly beneficial to vision-impaired older adults.

Resilience resources may buffer some middle-aged and older Black Americans from memory decline despite experiencing discrimination

RATIONALE

Experiences of discrimination have been associated with poorer episodic memory in Black Americans. However, resilience resources at multiple levels (individual, social, and endowed) may act as a buffer to protect future memory decline, especially in the face of discrimination.

OBJECTIVE

Using longitudinal data from the 2006-2016 Health and Retirement Study (N = 1862), we tested whether Black Americans aged 50 and older would show different trajectories of episodic memory depending on their reported experiences of discrimination (everyday and major lifetime) and resilience resources.

METHODS

Analyses were conducted in three steps: (1) joint latent cluster mixed modeling (JLCMM) to estimate the number of classes, (2) barycentric discriminant analyses (BADA) to model the combined influence of discrimination and resilience resources between each memory class, and (3) multinomial regression analyses to explore interactions between discrimination and resilience resources.

RESULTS

JLCMM resulted in three memory classes that differentiated baseline from longitudinal memory performance: "High Decliners," "Low Decliners," and "Low Stable." Two independent patterns described the relationships between the three classes in the context of discrimination and resilience resources. First, compared with High Decliners, the two lower baseline memory classes (Low Decliners and Low Stable) reported more everyday discrimination and lower individual and endowed resilience resources. Second, although the Low Stable class did not report different levels of discrimination, they had more social resilience resources (greater social support and more social contact) than both declining classes.

CONCLUSIONS

Black Americans in later life have heterogeneous patterns of memory trajectories as demonstrated by the three memory classes identified. Those with lower baseline memory experienced more everyday discrimination and had fewer resilience resources compared to those with high baseline performance (High Decliners). Greater social resilience resources were associated with maintained episodic memory over time in Black Americans.

Financial hardship and change in emotional well-being before to during COVID-19 pandemic among middle-aged and older Americans: Moderating effects of internal coping resources

OBJECTIVE

The purpose of this study was to investigate associations between financial hardship and change in emotional well-being-positive and negative affect-before to during the COVID-19 pandemic among middle-aged and older Americans and to examine the extent to which associations were moderated by internal coping resources-dispositional mastery and optimism.

METHOD

Data derived from the Leave-Behind Questionnaire in the 2016 and 2020 waves of the Health and Retirement Study, a nationally representative longitudinal survey of U.S. adults aged 51 and older (N = 1312). We estimated multivariate ordinary least squares regression models with interaction terms to evaluate prospectively the benefits of mastery and optimism as internal coping resources for middle-aged and older adults.

RESULTS

Dispositional mastery moderated the effects of financial hardship on changes in negative and positive affect, respectively, before to during the COVID-19 pandemic; however, optimism did not significantly moderate the effects of financial hardship on change in negative and positive affect before to during the COVID-19 pandemic.

CONCLUSIONS

Our findings have implications for interventions aimed at improving middle-aged and older adults' emotional well-being by promoting internal coping resources. Specifically, interventions should focus on financial hardship and mastery for vulnerable middle-aged and older adults in the context of public health crises.

The Effect of Physical Limitations on Depressive Symptoms over the Life Course: Is Optimism a Protective Buffer?

OBJECTIVES

We examined the extent to which optimism buffers the effects of physical limitations on depressive symptoms, across four mid- and later-life age groups (ages 40-49, 50-64, 65-74, 75+ at baseline). Analyses are motivated by stress theories, which hold that the protective effects of coping resources are evidenced only at high levels of stress. We further explore whether these purportedly protective effects diminish with age, as health-related stressor(s) intensify and become irreversible.

METHODS

We use data from two waves (2004-06 and 2013-14) of the Health and Retirement Study (HRS, n = 4,515) and Midlife in the United States (MIDUS, n = 2,138). We estimate OLS regression models with three-way interaction terms to examine prospectively the benefits of optimism as a coping resource for persons with physical limitations across four age groups. Physical limitations are assessed with a composite measure encompassing mobility and activity of daily living (ADL) limitations.

RESULTS

In HRS and MIDUS, persons with 3+ limitations reported significantly more depressive symptoms than persons with 0-2 limitations, yet these disparities diminished at higher levels of optimism. Buffering effects of optimism vary by age. For midlife and young-old persons with 3+ limitations, optimism is strongly and inversely related to depressive symptoms at follow-up. Comparable protective effects are not evident among oldest sample members.

DISCUSSION

Stress and coping models should consider more fully factors that limit older adults' capacity to deploy purportedly protective personal resources. Investments in structural or institutional supports may be more effective than interventions to enhance positive thinking.

How widowhood status relates to engagement in advance care planning among older adults: does race/ethnicity matter?

OBJECTIVES

This study investigated whether and to what extent widowhood status is related to engagement in advance care planning (ACP), and further whether race/ethnicity moderated the relation.

METHODS

We analyzed a total of 11,257 older Americans from the Health and Retirement Study using random-effect regression models after controlling for covariates and year-fixed effects.

RESULTS

We found that both being a widow/widower ever and having been widowed for a longer period of time were associated with a higher probability of engagement in ACP. Specifically, we found that a one-year increase in the number of years since spousal death was associated with 1.02 (p < 0.05, 95% CI = 1.00, 1.03) changes in the odds ratios of informal ACP; however, inclusion of a quadratic term indicated that this association reversed after the peak. Moreover, our findings suggested a moderating effect of race/ethnicity on the relations of the length of time since spousal loss with engagement in ACP. Specifically, the odds of widowed non-Hispanic Blacks discussing with someone the care or medical treatment (informal ACP) and having a living will (formal ACP) were 0.96 (p < 0.05, 95% CI = 0.93, 1.00) and 0.88 (p < 0.05, 95% CI = 0.79, 0.97) times that of non-widowed non-Hispanic Whites. Compared with their non-Hispanic White counterparts, widowed non-Hispanic Blacks were less likely to engage in ACP, and the negative relations were exacerbated when they became widows/widowers.

CONCLUSION

We elaborated on these findings and discussed their implications for understanding the moderating effect of race/ethnicity on the relation between late-life widowhood and engagement in ACP. In order to develop programs that enhance engagement in ACP and reduce racial/ethnic disparities, research must incorporate intersectionality theory with attention to motivations and decision-making style among diverse widows/widowers. The findings from this study could help inform policy makers when developing public health programs and health care reimbursement programs that enhance engagement in ACP among widows/widowers.

Personality and compliance with COVID-19 protective measures among older Americans: Moderating effects of age, gender, and race/ethnicity

Following the growing evidence that personality is related to various health behaviors, we examined whether personality traits were related to compliance with COVID-19 protective measures and evaluated the extent to which associations were moderated by age, gender, or race/ethnicity among older adults during a summer 2020 surge of COVID-19 cases in the United States. Data were from the 2020 Health and Retirement Study COVID-19 module. Multivariate ordinary least squares regression analyses were computed adjusting for health, psychosocial, and sociodemographic factors. Results indicated the significant associations between personality traits and compliance with COVID-19 measures varied by age, gender, and race/ethnicity. Specifically, the associations of agreeableness with wearing a mask and frequent handwashing were less pronounced among older compared with younger individuals. The association between extraversion and wearing masks was stronger for men than for women. The associations of agreeableness with handwashing and physical distancing were weaker for Hispanic older adults, whereas the associations of extraversion with physical distancing and using sanitizers were stronger for Hispanic older adults than for their non-Hispanic White counterparts. Implications regarding behavioral science underlying the current pandemic and future public health crises are discussed.

The Impact of the COVID-19 Pandemic on Business Ownership Across Racial/Ethnic Groups and Gender

This study examined the economic impact of the COVID-19 pandemic on US older entrepreneurs' businesses using the Health and Retirement Study. We estimated logistic regression models to document the odds of experiencing economic impact. The COVID-19 pandemic has affected nearly 76% of US older entrepreneurs but has disproportionately impacted the businesses of Black, Hispanic, Asian/other races, and women entrepreneurs. Older Black entrepreneurs had significantly higher odds of facing business closure (OR = 2.31, p < .01), implementing new procedures (OR = 2.44, p < .01), workers quitting (OR = 2.95, p < .001), and difficulty paying regular bills (OR = 2.88, p < .001) than their White counterparts. Older Hispanic entrepreneurs also had significantly higher odds of instituting new procedures (OR = 2.27, p < .05), workers quitting (OR = 2.26, p < .01), and difficulty paying regular bills (OR = 2.35, p < .01) than their White counterparts. Similarly, older Asian/other races entrepreneurs were significantly more likely to report difficulty paying regular bills since the start of the pandemic than their White counterparts (OR = 3.11, p < .01). Women entrepreneurs were significantly more likely to close their businesses than their male counterparts (OR = 2.11, p < .001). These significant associations persisted after controlling for confounders. Support for underserved racial/ethnic groups and older women entrepreneurs should focus on accessibility to financial services, capital, and support packages as well as legislative support for ensuring business continuity and success.

Food insecurity associated with higher COVID-19 infection in households with older adults

OBJECTIVES

As a well-documented social determinant of health, food insecurity may be associated with COVID-19 infection in households with older adults. We examined whether older adults were vulnerable to COVID-19 infection during the early pandemic if they were food insecure versus food secure.

STUDY DESIGN

A cross-sectional study using a nationally representative population-based survey of US older adults.

METHODS

We used a random subsample of Health and Retirement Study (HRS) drawn in June 2020 (N = 3212). We compared the odds of reporting COVID-19 infection in a household, COVID-19 infection and mortality among acquaintances, and respondent's perceived fair or poor health across household food insecurity status resulted from financial or non-financial barriers. Baseline health and socioeconomic circumstances were adjusted in the models.

RESULTS

Results showed a higher COVID-19 infection rate among food-insecure households than among their food-secure counterparts during the pandemic. Food insecurity due to non-financial obstacles was associated with greater likelihood of COVID-19 infection both within respondents' households (adjusted odds ratio [aOR] = 1.73, 95% confidence interval [CI]: 1.03-2.90) and among their acquaintances (aOR = 1.32, 95% CI: 1.05-1.65). Food insecurity caused by both non-financial and financial constraints was associated with twice the likelihood of knowing someone who died from COVID-19 than their food-secure counterparts (aOR = 2.14, 95% CI: 1.27-3.61).

CONCLUSIONS

Food insecurity driven by non-financial constraints played an important role in the ongoing pandemic among US older adults. Policies addressing COVID-19 need to recognize the vulnerability of food-insecure older adults beyond lack of monetary resources.

Physical Disability and Older Adults' Perceived Food and Economic Insecurity During the COVID-19 Pandemic

OBJECTIVES

We examined whether older adults with physical disability were vulnerable to three types of perceived economic insecurity (difficulty paying regular bills, difficulty paying medical bills, income loss) and two types of perceived food insecurity (economic obstacles, logistical obstacles) during the early months of the COVID-19 pandemic. We evaluated the extent to which associations are moderated by three personal characteristics (age, sex, race/ethnicity) and two pandemic-specific risk factors (job loss, COVID-19 diagnosis).

METHODS

Data are from a random 25 percent subsample of Health and Retirement Study (HRS) participants who completed a COVID-19 module introduced in June 2020. We estimated logistic regression models to predict each of five self-reported hardships during the pandemic.

RESULTS

Bivariate analyses showed that persons with three or more functional limitations were more likely to report both types of food insecurity, and difficulty paying regular and medical bills since the start of the pandemic, relative to those with no limitations. After controlling for health conditions, effects were no longer significant for paying medical bills, and attenuated yet remained statistically significant for other outcomes. Patterns did not differ significantly on the basis of the moderator variables. Job loss substantially increased the risk of economic insecurity but not food insecurity.

DISCUSSION

Older adults with more functional limitations were vulnerable to economic and food insecurity during the pandemic, potentially exacerbating the physical and emotional health threats imposed by COVID-19. Supports for older adults with disability should focus on logistical as well as financial support for ensuring their food security.

Reduced peripheral activity leading to hepato-preferential action of basal insulin peglispro compared with insulin glargine in patients with type 1 diabetes

AIMS

Basal insulin peglispro (BIL), a novel PEGylated basal insulin with a large hydrodynamic size, has a delayed absorption and reduced clearance that prolongs the duration of action. The current study compared the effects of BIL and insulin glargine (GL) on endogenous glucose production (EGP), glucose disposal rate (GDR) and lipolysis in patients with type 1 diabetes.

MATERIALS AND METHODS

This was a randomized, open-label, four-period, crossover study. Patients received intravenous infusions of BIL and GL, each at two dose levels selected for partial and maximal suppression of EGP, during an 8 to 10 h euglycemic clamp procedure with d-[3-³ H] glucose.

RESULTS

Following correction for equivalent human insulin concentrations (EHIC), low-dose GL infusion resulted in similar EGP at the end of the clamp compared to low-dose BIL infusion (GL/BIL ratio of 1.03) but a higher GDR (GL/BIL ratio of 2.42), indicating similar hepatic activity but attenuated peripheral activity of BIL. Consistent with this, the EHIC-corrected GDR/EGP at the end of the clamp was 1.72-fold greater for GL than BIL following low-dose administration. At the lower dose of BIL and GL (concentrations in the therapeutic range), BIL produced less suppression of lipolysis compared with GL as indicated by free fatty acid and glycerol levels at the end of the clamp.

CONCLUSIONS

Compared with GL, BIL restored the hepato-peripheral insulin action gradient seen in normal physiology via its peripherally restricted action on target tissues related to carbohydrate and lipid metabolism.

Phase 3, open-label, randomized study of the pharmacokinetics, efficacy and safety of ixekizumab following subcutaneous administration using a prefilled syringe or an autoinjector in patients with moderate-to-severe plaque psoriasis (UNCOVER-A)

Background

The efficacy of ixekizumab, an anti‐interleukin‐17A (anti‐IL‐17A) monoclonal IgG4 antibody, was demonstrated in moderate‐to‐severe psoriasis patients when administered via prefilled syringe (PFS).

Objective

To evaluate the effect of two drug delivery devices on the pharmacokinetics (PK) of ixekizumab as well as efficacy and safety with both devices.

Methods

In the first 12 weeks of an open‐label, phase 3 study, moderate‐to‐severe psoriasis patients were randomized to ixekizumab delivery via PFS or autoinjector device. Randomization was stratified by weight (<80 kg, 80–100 kg, >100 kg), injection assistance (yes/no) and injection site (arm, thigh or abdomen). Following a 160‐mg initial dose at week 0, patients received subcutaneous 80‐mg ixekizumab as a single injection every 2 weeks for 12 weeks. Blood samples were collected following the initial 160‐mg dose on days 2, 4, 7, 10 and 14 for PK analysis. Primary PK parameters were maximum concentration (C_max) and area under the curve (AUC_0‐tlast) where t_last is the time of last sample (14 days ± 24 h). Efficacy was assessed by percent improvement on the Psoriasis Area and Severity Index (PASI) at week 12. Adverse event reporting, vital signs and clinical laboratory data were used to evaluate safety.

Results

Of 204 randomized patients, 192 were included in the PK analysis (PFS: 94; autoinjector: 98). The PFS and autoinjector showed similar geometric mean C_max (90% CI) [15.0 μg/mL (13.9–16.1) vs. 14.8 μg/mL (13.8–15.9)] and geometric mean AUC_0‐tlast (90% CI) [157 μg × day/mL (147–168) vs. 154 μg × day/mL (144–165)]. When comparing C_max and AUC_0‐tlast of the autoinjector to PFS, the geometric LS mean ratios were 0.97. At week 12, mean percent PASI improvement (via modified baseline observation carried forward) was similar with the PFS (89.3%) and autoinjector (86.9%). Both devices had safety results that were consistent with the known safety profile of ixekizumab.

Conclusion

The PK, efficacy and safety of ixekizumab administered subcutaneously by PFS and autoinjector were similar.

Clinicaltrials.gov number: NCT01777191 https://clinicaltrials.gov/ct2/show/NCT01777191

Steady-state pharmacokinetics and glucodynamics of the novel, long-acting basal insulin LY2605541 dosed once-daily in patients with type 2 diabetes mellitus

AIMS

To assess the pharmacokinetics (PK) and glucodynamics (GD) of LY2605541 in patients with type 2 diabetes mellitus.

METHODS

This parallel-group, open-label, dose-escalation study examined the PK and GD of basal insulin LY2605541 after single and multiple-dose administration. Fixed doses of LY2605541 (0.33-1.00 U/kg) were given once-daily (QD) for 14 days to insulin-treated patients with type 2 diabetes. A 24-h euglycaemic glucose clamp was conducted on days 1 and 14.

RESULTS

PK steady state was achieved within 7-10 days and the peak-to-trough fluctuation was <2, translating to a nearly 'peakless' glucose infusion rate at steady state and with a duration of action of at least 24 h. Across dose levels t1/2 ranged from 44.7 to 75.5 h (~2-3 days). As steady state was achieved, there were dose-dependent reductions in the prandial insulin dose and in fasting blood glucose, which decreased to 60-100 mg/dl across dose levels. Within-patient variability was <14 and <26% for the area under the concentration versus time curve (AUC) of the 8-point blood glucose profile and fasting blood glucose, respectively. The nocturnal glucose control between 03:00 and 09:00 hours was relatively unchanged. Mild hypoglycaemia was the most common adverse event.

CONCLUSIONS

In this Phase I study of fixed LY2605541 doses without titration, LY2605541 was well-tolerated and demonstrated a flat PK and GD profile accompanied by glucose normalization, prandial insulin dose reduction and no severe hypoglycaemia.

The regulation of AMP-activated protein kinase by H(2)O(2)

AMP-activated protein kinase (AMPK), a heterotrimeric serine/threonine kinase, is activated by conditions leading to an increase of the intracellular AMP:ATP ratio. However, how AMPK is regulated under the oxidative stress is completely unknown. In the present study, we examined effects of the oxidative agent H(2)O(2) on AMPK. AMPK was transiently and concentration-dependently activated by H(2)O(2) in NIH-3T3 cells. This activation was tightly associated with an increased AMP:ATP ratio, an electrophoretic mobility shift of AMPK alpha1 catalytic subunit, and an increased phosphorylation level of AMPK alpha1 threonine 172, which is a major in vitro phosphorylation site by the upstream AMPK kinase. All of these events were significantly blocked by the pretreatment of 0.5% dimethyl sulfoxide, a potent hydroxyl radical scavenger, indicating that AMPK cascades are highly sensitive to the oxidative stress. Interestingly, a specific tyrosine kinase inhibitor, genistein, further stimulated the H(2)O(2)-induced AMPK activity by 70% without altering the AMP:ATP. Taken together, our results suggest that AMP:ATP ratio is the major parameter to which AMPK responds under the oxidative stress, but AMPK may be regulated in part by a tyrosine kinase-dependent pathway, which is independent of the cellular adenosine nucleotides level.

Effects of stimulation of AMP-activated protein kinase on insulin-like growth factor 1- and epidermal growth factor-dependent extracellular signal-regulated kinase pathway

AMP-activated protein kinase (AMPK) is tightly regulated by the cellular AMP:ATP ratio and plays a central role in the regulation of energy homeostasis. Previously, AMPK was reported to phosphorylate serine 621 of Raf-1 in vitro. In the present study, we investigated a possible role of AMPK in extracellular signal-regulated kinase (Erk) cascades, using 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR), a cell-permeable activator of AMPK and antisense RNA experiments. Activation of AMPK by AICAR in NIH-3T3 cells resulted in drastic inhibitions of Ras, Raf-1, and Erk activation induced by insulin-like growth factor 1 (IGF-1). Expression of an antisense RNA for the AMPK catalytic subunit decreased the AMPK activity and significantly diminished the AICAR effect on IGF-1-induced Ras activation and the subsequent Erk activation, indicating that its effect is indeed mediated by AMPK. Phosphorylation of Raf-1 serine 621, however, was not involved in AMPK-mediated inhibition of Erk cascades. In contrast to IGF-1, AICAR did not block epidermal growth factor (EGF)-dependent Raf-1 and Erk activation, but our results demonstrated that multiple Raf-1 upstream pathways induced by EGF were differentially affected by AICAR: inhibition of Ras activation and simultaneous induction of Ras-independent Raf activation. The activities of IGF-1 and EGF receptor were not affected by AICAR. Taken together, our results suggest that AMPK differentially regulate Erk cascades by inhibiting Ras activation or stimulating the Ras-independent pathway in response to the varying energy status of the cell.

Phosphatidylinositol 3-kinase stimulates muscle differentiation by activating p38 mitogen-activated protein kinase

The activation of both phosphatidylinositol 3-kinase (PI3-kinase) and p38 mitogen-activated protein kinase (p38 MAPK) is required for muscle differentiation. However, it is not known whether the signals from these two kinases interact during this process. In this work, we have investigated this using H9c2 cardiac myoblasts. The p38 MAPK-specific inhibitor SB203580 blocked muscle differentiation and suppressed the expression of myogenin and myosin heavy chain in a concentration-dependent manner. Consistent with this, expression of a wild-type p38 MAPK (Ha-p38) or a constitutively active MAPK kinase 6 (MKK6(glu)) promoted the rate of differentiation into multinucleated myotubes. LY294002, a PI3-kinase inhibitor, suppressed in a dose-dependent manner not only muscle differentiation but also activation of p38 MAPK. In addition, expression of a constitutively active form of PI3-kinase (p110*) enhanced myotube formation and p38 MAPK activation, while expression of a dominant negative form of PI3-kinase (Deltap85) attenuated these responses. Furthermore, SB203580 suppressed differentiation of H9c2 cells expressing p110*. Interestingly, LY294002 also suppressed differentiation of H9c2 cells expressing Ha-p38 or MKK6(glu). However, SB203580 did not affect PI3-kinase activity, suggesting that PI3-kinase myogenic signaling to p38 MAPK is unidirectional. Taken together, we concluded that PI3-kinase activates p38 MAPK, which in turn stimulates muscle differentiation, but that p38 MAPK does not substitute for PI3-kinase in this process.

Mannan-binding lectin (MBL)-associated plasma protein present in human urine inhibits calcium oxalate crystal growth

Mannan-binding lectin (MBL)-associated plasma protein (MAp19) is an alternatively spliced form of MBL-associated serine protease-2, a component of a complement activation cascade. We observed that MAp19 is excreted in human urine. Interestingly, the amount of MAp19 was higher in urine of renal cell carcinoma patients than healthy people. Pretreatment of urine dialysate with 50 mM EDTA increased the recovery of MAp19, suggesting that MAp19 is a calcium-binding protein. The recombinant MAp19 showed a strong inhibition of calcium oxalate crystal growth in vitro in a concentration-dependent manner. Thus, we conclude that MAp19 plays a role in the inhibition of calcium oxalate renal stone formation.

The regulatory mechanism of phosphatidylinositol 3-kinase by insulin in 3T3 L1 fibroblasts: phosphorylation-independent activation of phosphatidylinositol 3-kinase

Phosphatidylinositol (PI) 3-kinase plays an important role in transducing the signals of various growth factor receptors. However, the regulatory mechanism of PI3-kinase activity by these growth factor receptors is not completely understood. Therefore, we attempted to clarify the regulatory mechanism of PI3-kinase using insulin and 3T3 L1 fibroblasts. Our results showed that insulin stimulated PI3-kinase activity seven-fold and concomitantly phosphorylated a p85 subunit at the tyrosine residue. However, this tyrosine phosphorylation was not significant in the activation of PI3-kinase as the PI3-kinase pulled down by the overexpressed GST-p85 fusion protein showed as high an activity as the immunoprecipitated one. The p110 subunit was phosphorylated at both serine and tyrosine residues without insulin treatment. Since the phosphorylation state was not changed by insulin. The results suggested that phosphorylation of the p110 subunit does not control PI3-kinase activity. Finally, it was shown that the insulin receptor substrate-1 (IRS-1) binding to PI3-kinase was not sufficient for full activation because the amount of IRS-1 pulled down by the GST-p85 fusion protein reached almost maximum, after incubation with insulin-treated cell lysates for 20 min, whereas PI3-kinase activity reached its maximum only after incubation for 5 h. All results suggest that the phosphorylation of p85 subunit at tyrosine residues and phosphorylation of p110 subunit at tyrosine or serine residues are not functionally significant in the regulation of PI3-kinase activity. They also suggest that P13-kinase is needed to bind to other protein(s) as well as the insulin receptor substrate-1 for full activation.